| Author |
Message |
Steve Cousins
Guest
|
 Posted:
Tue Oct 11, 2005 11:44 pm Post subject:
Re: DLT or LTO or AIT for new tape drive? |
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Curious George wrote:
[quote]On Fri, 07 Oct 2005 10:52:14 -0400, Steve Cousins
steve.cousins@maine.edu> wrote:
SDLT, DLT 8000, and most LTO drives have variable speed capability. The
only LTO's that don't seem to have it are HP and IBM versions of LTO1.
Then why is it only advertized in Seagate LTO-1 and newer HP & IBM
LTO-2's?
[/quote]
I'm not sure what you are implying. Are you saying that you think that
DLT 8000 and SDLT's don't have it? I specified that HP and IBM LTO1
didn't have it, which leaves Seagate that does have it. Maybe there are
some (older?) HP and IBM LTO-2's that don't have it. You could be right
about that I don't know. |
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Curious George
Guest
|
| Posted:
Wed Oct 12, 2005 7:26 am Post subject:
Re: DLT or LTO or AIT for new tape drive? |
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On Tue, 11 Oct 2005 14:44:53 -0400, Steve Cousins
<steve.cousins@maine.edu> wrote:
[quote]I'm not sure what you are implying.
[/quote]
That AFAIK advertized specs & manuals don't corroborate that claim for
DLT 8000, SDLT's, & several early model LTO-2's. Would you mind
giving an official reference for either DLT flavor for this feature? |
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Steve Cousins
Guest
|
| Posted:
Wed Oct 12, 2005 11:52 pm Post subject:
Re: DLT or LTO or AIT for new tape drive? |
|
|
Curious George wrote:
[quote]On Tue, 11 Oct 2005 14:44:53 -0400, Steve Cousins
steve.cousins@maine.edu> wrote:
I'm not sure what you are implying.
That AFAIK advertized specs & manuals don't corroborate that claim for
DLT 8000, SDLT's, & several early model LTO-2's. Would you mind
giving an official reference for either DLT flavor for this feature?
There are these things called Search Engines that help a lot with this[/quote]
sort of thing ;^):
Check out: http://downloads.quantum.com/dlt8000/dlt8000productmanual.pdf
As far as I know, all SDLT drives after this included this feature,
however, you are correct that it doesn't seem to be in the literature.
I found that SDLT-600 does have it but possibly the SDLT-220 does not.
In any event, whether it is due to better buffering or some sort of
variable speed, I get no shoe-shining when backing up over 100 Mbps
network on a SDLT 220 drive. It may be theoretically possible to get
11MB/sec on a 100 Mbps connection but it is cutting it very close and
the SDLT is doing something to compensate. Further, I find it odd that
they would have had this feature on the DLT-8000 but not on SDLT-1.
As for LTO-1: http://www.certance.com/products/lto-ultrium/lto1/STU62001LW-K
LTO-2:
Certance: http://www.certance.com/products/lto-ultrium/lto2/CL1002-SS
IBM:
http://www.exabyte.com/support/online/documentation/whitepapers/ibmlto-2overview.pdf
HP: http://h18006.www1.hp.com/products/storageworks/esl9000/qa.html#1
Each vendor calls it something different: FastSense, Digital Speed
Matching (DSM) and Adaptive Tape Speed (ATS) from Certance, IBM and HP
respecitively.
Actually, the HP link indicates that it was available even on LTO-1 so
it looks like IBM LTO-1 was the only version not to have this feature. |
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Curious George
Guest
|
| Posted:
Thu Oct 13, 2005 10:23 pm Post subject:
Re: DLT or LTO or AIT for new tape drive? |
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|
On Wed, 12 Oct 2005 14:52:59 -0400, Steve Cousins
<steve.cousins@maine.edu> wrote:
| Quote: | Curious George wrote:
On Tue, 11 Oct 2005 14:44:53 -0400, Steve Cousins
steve.cousins@maine.edu> wrote:
I'm not sure what you are implying.
That AFAIK advertized specs & manuals don't corroborate that claim for
DLT 8000, SDLT's, & several early model LTO-2's. Would you mind
giving an official reference for either DLT flavor for this feature?
There are these things called Search Engines that help a lot with this
sort of thing ;^):
|
Naw. Ya think? So the secret to avoiding such criticism is to just
write "Nope" or "Clueless" ; )
Actually here's a link I didn't see earlier in the conversation or the
past:
http://tinyurl.com/9e9ge
According to this SDLT does do it using "Digital Data Rate Agent"
(DDRA). It claims it was first introduced in the SDLT 220 (not the
DLT 8000). I thought the SDLT 220 didn't have it. That appears
wrong.
did that before the last post & other times in the past. Don't see
anything that resembles the feature. The user man refers to an
"adaptive control mechanism" & "Dual Speed Recording" but AFAIK
neither is a "variable speed" feature. I'd love to be proven wrong
and be able to implement a feature I've been neglecting to use from
ignorance.
| Quote: | As far as I know, all SDLT drives after this included this feature,
however, you are correct that it doesn't seem to be in the literature.
I found that SDLT-600 does have it but possibly the SDLT-220 does not.
|
SDLT600 is newest/best and not necessarily indicative of the whole
SDLT line (e.g. DLT ICE). Apparently DDRA is part of the whole SDLT
line anyway.
True it isn't really in the literature. even a search of Quantum's
knowledge base of "DDRA," "Digital Data Rate Agent," (or parts of that
term) ,"variable speed" etc, turns up no hits. My searches of manuals
look the same. It makes no sense to me Quantum would want to hide
this feature.
| Quote: | In any event, whether it is due to better buffering or some sort of
variable speed, I get no shoe-shining when backing up over 100 Mbps
network on a SDLT 220 drive. It may be theoretically possible to get
11MB/sec on a 100 Mbps connection but it is cutting it very close and
the SDLT is doing something to compensate.
|
Buffering is a major factor. Without enabling the DDRA it's very
possible to backup over 100Mbs near / just shy of full speed. That
means basically a good stream with some very infrequent stops (perhaps
too infrequent to notice?) but definitely not bad shoe-shining per se.
| Quote: | Further, I find it odd that
they would have had this feature on the DLT-8000 but not on SDLT-1.
|
But I'm not convinced it is on the DLT 8000. The manual's timing
specs show fixed rates with no discussion of DDRA or similar. But
then who can trust the manual. : (
I'm not sure I agree it is _so_ unlikely a feature could be present,
dropped, and not picked up again until a generation or two later. It
wouldn't be the first time someone had trouble with a "new" feature
that wasn't playing well with the next new reworked design and it had
to be put on the shelf until the kinks were worked out.
I always agreed Seagate/Certance had this since LTO-1
Those are recent HP LTO's
| Quote: | Each vendor calls it something different: FastSense, Digital Speed
Matching (DSM) and Adaptive Tape Speed (ATS) from Certance, IBM and HP
respecitively.
Actually, the HP link indicates that it was available even on LTO-1 so
it looks like IBM LTO-1 was the only version not to have this feature.
|
HP Ultrium 215 did not have it (LTO-1). It was introduced in the 230.
I thought there was an IBM LTO-2 without it also, but cannot recall
the model #. |
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Steve Cousins
Guest
|
| Posted:
Thu Oct 13, 2005 11:28 pm Post subject:
Re: DLT or LTO or AIT for new tape drive? |
|
|
Curious George wrote:
| Quote: | On Wed, 12 Oct 2005 14:52:59 -0400, Steve Cousins
steve.cousins@maine.edu> wrote:
There are these things called Search Engines that help a lot with this
sort of thing ;^):
Naw. Ya think? So the secret to avoiding such criticism is to just
write "Nope" or "Clueless" ; )
Or doing more digging. You're right though to an extent. It took longer |
than I expected to find the references to this ubiquitous feature. Sorry
for the cheap jab.
| Quote: | Actually here's a link I didn't see earlier in the conversation or the
past:
http://tinyurl.com/9e9ge
According to this SDLT does do it using "Digital Data Rate Agent"
(DDRA). It claims it was first introduced in the SDLT 220 (not the
DLT 8000). I thought the SDLT 220 didn't have it. That appears
wrong.
Check out: http://downloads.quantum.com/dlt8000/dlt8000productmanual.pdf
did that before the last post & other times in the past. Don't see
anything that resembles the feature. The user man refers to an
"adaptive control mechanism" & "Dual Speed Recording" but AFAIK
neither is a "variable speed" feature. I'd love to be proven wrong
and be able to implement a feature I've been neglecting to use from
ignorance.
Search the document for "variable" and the first mention of it is that |
they changed the term "Variable Speed Recording" to "Dual Speed
Recording". It doesn't specify the range though so who knows?
| Quote: | As far as I know, all SDLT drives after this included this feature,
however, you are correct that it doesn't seem to be in the literature.
I found that SDLT-600 does have it but possibly the SDLT-220 does not.
SDLT600 is newest/best and not necessarily indicative of the whole
SDLT line (e.g. DLT ICE). Apparently DDRA is part of the whole SDLT
line anyway.
True it isn't really in the literature. even a search of Quantum's
knowledge base of "DDRA," "Digital Data Rate Agent," (or parts of that
term) ,"variable speed" etc, turns up no hits. My searches of manuals
look the same. It makes no sense to me Quantum would want to hide
this feature.
In any event, whether it is due to better buffering or some sort of
variable speed, I get no shoe-shining when backing up over 100 Mbps
network on a SDLT 220 drive. It may be theoretically possible to get
11MB/sec on a 100 Mbps connection but it is cutting it very close and
the SDLT is doing something to compensate.
Buffering is a major factor. Without enabling the DDRA it's very
possible to backup over 100Mbs near / just shy of full speed. That
means basically a good stream with some very infrequent stops (perhaps
too infrequent to notice?) but definitely not bad shoe-shining per se.
Could be. It runs pretty smoothly in any case. With TCP overhead, 11 |
MB is more like 110 Mb so even with 100% utilization of the the network
channel there would still be a 10% overrun. I can't believe it would
stream this well, even with some buffering, without it changing speed to
match the data coming in.
| Quote: | Further, I find it odd that
they would have had this feature on the DLT-8000 but not on SDLT-1.
But I'm not convinced it is on the DLT 8000. The manual's timing
specs show fixed rates with no discussion of DDRA or similar. But
then who can trust the manual. : (
I'm not sure I agree it is _so_ unlikely a feature could be present,
dropped, and not picked up again until a generation or two later. It
wouldn't be the first time someone had trouble with a "new" feature
that wasn't playing well with the next new reworked design and it had
to be put on the shelf until the kinks were worked out.
As for LTO-1: http://www.certance.com/products/lto-ultrium/lto1/STU62001LW-K
LTO-2:
Certance: http://www.certance.com/products/lto-ultrium/lto2/CL1002-SS
I always agreed Seagate/Certance had this since LTO-1
Just trying to create a complete record. |
Q1. Does Ultrium 960 FC tape drive support Adaptive Tape Speed (ATS)?
A1. Yes, the HP StorageWorks Ultrium 960 FC tape drives available
throughout the entire ESL portfolio do carry forward the ATS technology
from the HP StorageWorks Ultrium 460 and 960 tape drives. The range for
the second generation of drives was from 10-30 MB/sec; for the HP
StorageWorks Ultrium 960 FC tape drive the range is 27-80 MB/sec.
So, the Ultrium 460 (LTO-2) has a range of 10 MB/sec to 30 MB/sec.
| Quote: | Each vendor calls it something different: FastSense, Digital Speed
Matching (DSM) and Adaptive Tape Speed (ATS) from Certance, IBM and HP
respecitively.
Actually, the HP link indicates that it was available even on LTO-1 so
it looks like IBM LTO-1 was the only version not to have this feature.
HP Ultrium 215 did not have it (LTO-1).
Actually it did. From 6 MB/sec to 7.5 MB/sec: |
http://h18006.www1.hp.com/products/quickspecs/12128_div/12128_div.html
| Quote: | It was introduced in the 230.
Clueless. (I'm just kidding!) See above. |
| Quote: | I thought there was an IBM LTO-2 without it also, but cannot recall
the model #.
|
Bottom line: DLT-8000, SDLT, and LTO drives have this feature except
the IBM LTO-1. I haven't any experience with the Tandberg versions of
these drives. I'm guessing they have this feature too from what little
I've seen of their products. |
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Curious George
Guest
|
| Posted:
Fri Oct 14, 2005 2:03 am Post subject:
Re: DLT or LTO or AIT for new tape drive? |
|
|
On Thu, 13 Oct 2005 14:28:25 -0400, Steve Cousins
<steve.cousins@maine.edu> wrote:
| Quote: | Curious George wrote:
On Wed, 12 Oct 2005 14:52:59 -0400, Steve Cousins
steve.cousins@maine.edu> wrote:
There are these things called Search Engines that help a lot with this
sort of thing ;^):
Naw. Ya think? So the secret to avoiding such criticism is to just
write "Nope" or "Clueless" ; )
Or doing more digging. You're right though to an extent. It took longer
than I expected to find the references to this ubiquitous feature. Sorry
for the cheap jab.
|
Naw. I walked right into it.
I still don't understand, and don't believe we've successfully
answered, why such a useful feature would be so obscured to even
require "more digging." That _should_ be a significant selling point.
Unless there is a conspiracy to promote LTO. 8-P
| Quote: | Actually here's a link I didn't see earlier in the conversation or the
past:
http://tinyurl.com/9e9ge
According to this SDLT does do it using "Digital Data Rate Agent"
(DDRA). It claims it was first introduced in the SDLT 220 (not the
DLT 8000). I thought the SDLT 220 didn't have it. That appears
wrong.
Check out: http://downloads.quantum.com/dlt8000/dlt8000productmanual.pdf
did that before the last post & other times in the past. Don't see
anything that resembles the feature. The user man refers to an
"adaptive control mechanism" & "Dual Speed Recording" but AFAIK
neither is a "variable speed" feature. I'd love to be proven wrong
and be able to implement a feature I've been neglecting to use from
ignorance.
Search the document for "variable" and the first mention of it is that
they changed the term "Variable Speed Recording" to "Dual Speed
Recording". It doesn't specify the range though so who knows?
|
I always read "Dual Speed Recording" to mean data rate with
compression vs without. That is a poor & confusing term if it indeed
is supposed to imply "variable speed" i.e. "on-the-fly speed
adjustment"
Aha! I see now what you mean in the Revision History"
Manual Number - Revision Level :81-60118-03 :
"Modified references to variable speed recording (now called Dual
Speed). Added new tape speed specs,"
So how did my acrobat searches of "variable speed" turn up nothing?"
I'm slipping I guess.
| Quote: | As far as I know, all SDLT drives after this included this feature,
however, you are correct that it doesn't seem to be in the literature.
I found that SDLT-600 does have it but possibly the SDLT-220 does not.
SDLT600 is newest/best and not necessarily indicative of the whole
SDLT line (e.g. DLT ICE). Apparently DDRA is part of the whole SDLT
line anyway.
True it isn't really in the literature. even a search of Quantum's
knowledge base of "DDRA," "Digital Data Rate Agent," (or parts of that
term) ,"variable speed" etc, turns up no hits. My searches of manuals
look the same. It makes no sense to me Quantum would want to hide
this feature.
In any event, whether it is due to better buffering or some sort of
variable speed, I get no shoe-shining when backing up over 100 Mbps
network on a SDLT 220 drive. It may be theoretically possible to get
11MB/sec on a 100 Mbps connection but it is cutting it very close and
the SDLT is doing something to compensate.
Buffering is a major factor. Without enabling the DDRA it's very
possible to backup over 100Mbs near / just shy of full speed. That
means basically a good stream with some very infrequent stops (perhaps
too infrequent to notice?) but definitely not bad shoe-shining per se.
Could be. It runs pretty smoothly in any case. With TCP overhead, 11
MB is more like 110 Mb so even with 100% utilization of the the network
channel there would still be a 10% overrun. I can't believe it would
stream this well, even with some buffering, without it changing speed to
match the data coming in.
|
it isn't usually so smooth. not out of the box anyway. Unless I've
just been masking a broken/misconfigured SDLT220 with tweaks or
expecting a wider range of variable speeds than exists. It doesn't
sound like you did anything special to enable "variable speed/dual
speed recording." Is that true?
| Quote: | Further, I find it odd that
they would have had this feature on the DLT-8000 but not on SDLT-1.
But I'm not convinced it is on the DLT 8000. The manual's timing
specs show fixed rates with no discussion of DDRA or similar. But
then who can trust the manual. : (
I'm not sure I agree it is _so_ unlikely a feature could be present,
dropped, and not picked up again until a generation or two later. It
wouldn't be the first time someone had trouble with a "new" feature
that wasn't playing well with the next new reworked design and it had
to be put on the shelf until the kinks were worked out.
As for LTO-1: http://www.certance.com/products/lto-ultrium/lto1/STU62001LW-K
LTO-2:
Certance: http://www.certance.com/products/lto-ultrium/lto2/CL1002-SS
I always agreed Seagate/Certance had this since LTO-1
Just trying to create a complete record.
IBM:
http://www.exabyte.com/support/online/documentation/whitepapers/ibmlto-2overview.pdf
HP: http://h18006.www1.hp.com/products/storageworks/esl9000/qa.html#1
Those are recent HP LTO's
Here is what it says:
Q1. Does Ultrium 960 FC tape drive support Adaptive Tape Speed (ATS)?
A1. Yes, the HP StorageWorks Ultrium 960 FC tape drives available
throughout the entire ESL portfolio do carry forward the ATS technology
from the HP StorageWorks Ultrium 460 and 960 tape drives. The range for
the second generation of drives was from 10-30 MB/sec; for the HP
StorageWorks Ultrium 960 FC tape drive the range is 27-80 MB/sec.
So, the Ultrium 460 (LTO-2) has a range of 10 MB/sec to 30 MB/sec.
|
Right and the 460 & 960 are more recent LTO-2's like I've been saying.
| Quote: | Each vendor calls it something different: FastSense, Digital Speed
Matching (DSM) and Adaptive Tape Speed (ATS) from Certance, IBM and HP
respecitively.
Actually, the HP link indicates that it was available even on LTO-1 so
it looks like IBM LTO-1 was the only version not to have this feature.
HP Ultrium 215 did not have it (LTO-1).
Actually it did. From 6 MB/sec to 7.5 MB/sec:
http://h18006.www1.hp.com/products/quickspecs/12128_div/12128_div.html
It was introduced in the 230.
Clueless. (I'm just kidding!) See above.
|
Yes that implies it is a part of the entire family. as does this:
http://www.hp.com/products1/storage/products/tapebackup/ultrium_tapedrives/ultrium215/index.html
Yet this doesn't:
http://tinyurl.com/9e9ge
and I've seen the mistake repeated elsewhere in the past.
| Quote: | I thought there was an IBM LTO-2 without it also, but cannot recall
the model #.
Bottom line: DLT-8000, SDLT, and LTO drives have this feature except
the IBM LTO-1.
|
The bottom bottom line. There is a lot of misinformation & confusing
terminology surround this feature. One shouldn't (I didn't anyway)
expect such a useful feature to be obscured by terms like "Dual Speed
Recording", lack or prominence, etc. or for such erroneous history
like @ DLTtape.com & its repetition elsewhere & with some vendors.
| Quote: | I haven't any experience with the Tandberg versions of
these drives. I'm guessing they have this feature too from what little
I've seen of their products.
|
The Tandberg etc. versions of the DLTs & autoloaders are supposed to
be "Quantum" drives. But I've been wrong a lot in this thread. |
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Steve Cousins
Guest
|
| Posted:
Fri Oct 14, 2005 2:48 am Post subject:
Re: DLT or LTO or AIT for new tape drive? |
|
|
Curious George wrote:
| Quote: | I still don't understand, and don't believe we've successfully
answered, why such a useful feature would be so obscured to even
require "more digging." That _should_ be a significant selling point.
Unless there is a conspiracy to promote LTO. 8-P
I agree. |
..
..
..
| Quote: | Could be. It runs pretty smoothly in any case. With TCP overhead, 11
MB is more like 110 Mb so even with 100% utilization of the the network
channel there would still be a 10% overrun. I can't believe it would
stream this well, even with some buffering, without it changing speed to
match the data coming in.
it isn't usually so smooth. not out of the box anyway. Unless I've
just been masking a broken/misconfigured SDLT220 with tweaks or
expecting a wider range of variable speeds than exists. It doesn't
sound like you did anything special to enable "variable speed/dual
speed recording." Is that true?
The only "special" things I do in the backup to the SDLT 220 are: |
Set compression on:
mt setdensity 145
use a larger block size than the default tar block size (512 KB instead
of 10KB):
tar cvbf 1024 /dev/tape files
This really helped speed things up a lot for me. It helped alot when I
was using a DLT 7000 too.
Since I do set hardware compression on with setdensity, this makes
another case that it has variable speed capabilities since with
compression, it wants up to 22 MB/sec. |
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Curious George
Guest
|
| Posted:
Sat Oct 15, 2005 6:45 am Post subject:
Re: DLT or LTO or AIT for new tape drive? |
|
|
On Thu, 13 Oct 2005 17:48:07 -0400, Steve Cousins
<steve.cousins@maine.edu> wrote:
<snip>
| Quote: | It doesn't
sound like you did anything special to enable "variable speed/dual
speed recording." Is that true?
The only "special" things I do in the backup to the SDLT 220 are:
Set compression on:
mt setdensity 145
use a larger block size than the default tar block size (512 KB instead
of 10KB):
tar cvbf 1024 /dev/tape files
This really helped speed things up a lot for me. It helped alot when I
was using a DLT 7000 too.
Since I do set hardware compression on with setdensity, this makes
another case that it has variable speed capabilities since with
compression, it wants up to 22 MB/sec.
|
Thanks for sharing that. But I don't quite follow what compression
has to do with variable speed. 22MB/sec should not mean the tape
moves 2x as fast. It is a theoretical/artifical rate assuming 2:1
compression. The data rates between 11MB/sec & 22MB/sec are due to
varying compression ratios, not actual tape speed. I'd assume
variable speed to come into play <11MB/sec (native) and be present
| Quote: | 11MB/sec only when data is very compressible.
|
Tape manufacturers always do this; state max compression (usually 2:1)
and pretend the tape holds 2x the capacity and works 2x as fast. It's
been done long before the variable speed we're talking about here was
common. |
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Steve Cousins
Guest
|
| Posted:
Mon Oct 17, 2005 7:58 pm Post subject:
Re: DLT or LTO or AIT for new tape drive? |
|
|
Curious George wrote:
| Quote: | The only "special" things I do in the backup to the SDLT 220 are:
Set compression on:
mt setdensity 145
use a larger block size than the default tar block size (512 KB instead
of 10KB):
tar cvbf 1024 /dev/tape files
This really helped speed things up a lot for me. It helped alot when I
was using a DLT 7000 too.
Since I do set hardware compression on with setdensity, this makes
another case that it has variable speed capabilities since with
compression, it wants up to 22 MB/sec.
Thanks for sharing that. But I don't quite follow what compression
has to do with variable speed. 22MB/sec should not mean the tape
moves 2x as fast.
Correct. However, with compression on and with very compressible data, |
the drive will require 22 MB/s to keep streaming. The tape speed stays
the same but now there is more demand from the network interface, and
SCSI bus for that matter. You are now trying to get somewhere around
220 Mb/s (raw ethernet) from your 100Mb/s network interface and
something has to give, so the tendency to "shoe-shine" is increased.
Rewording it: the tape drive now needs 22MB/sec to stream but the
network card can only deliver ~10MB/sec so the tape has to stop and wait
for the network card, unless it can vary the tape speed to slow down to
10MB/sec. The problem is just amplified when compression is used.
22MB/sec from a 10MB/sec pipe vs. 11MB/sec from the same 10 MB/sec pipe. |
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Curious George
Guest
|
| Posted:
Tue Oct 18, 2005 1:44 am Post subject:
Re: DLT or LTO or AIT for new tape drive? |
|
|
On Mon, 17 Oct 2005 10:58:08 -0400, Steve Cousins
<steve.cousins@maine.edu> wrote:
| Quote: | Since I do set hardware compression on with setdensity, this makes
another case that it has variable speed capabilities since with
compression, it wants up to 22 MB/sec.
Thanks for sharing that. But I don't quite follow what compression
has to do with variable speed. 22MB/sec should not mean the tape
moves 2x as fast.
Correct. However, with compression on and with very compressible data,
the drive will require 22 MB/s to keep streaming. The tape speed stays
the same but now there is more demand from the network interface, and
SCSI bus for that matter. You are now trying to get somewhere around
220 Mb/s (raw ethernet) from your 100Mb/s network interface and
something has to give, so the tendency to "shoe-shine" is increased.
Rewording it: the tape drive now needs 22MB/sec to stream but the
network card can only deliver ~10MB/sec so the tape has to stop and wait
for the network card, unless it can vary the tape speed to slow down to
10MB/sec. The problem is just amplified when compression is used.
22MB/sec from a 10MB/sec pipe vs. 11MB/sec from the same 10 MB/sec pipe.
|
But that still does not mean compression capabilities 'indicate' that
the drive 'has the ability to slow up automagically' when there are
throughput problems (i.e. variable speed).
I agree, though, that compression can make it easier for there to be a
scenario where demand exceeds throughput, and _if_ the tape has the
ability to slow it will. But if it doesn't it won't; it'll just
shoeshine. |
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Steve Cousins
Guest
|
| Posted:
Tue Oct 18, 2005 3:00 am Post subject:
Re: DLT or LTO or AIT for new tape drive? |
|
|
Curious George wrote:
| Quote: | But that still does not mean compression capabilities 'indicate' that
the drive 'has the ability to slow up automagically' when there are
throughput problems (i.e. variable speed).
Yes. I never meant to imply that compression indicates variable tape |
speed. What I said was:
"Since I do set hardware compression on with setdensity, this makes
another case that it has variable speed capabilities since with
compression, it wants up to 22 MB/sec."
| Quote: | I agree, though, that compression can make it easier for there to be a
scenario where demand exceeds throughput, and _if_ the tape has the
ability to slow it will. But if it doesn't it won't; it'll just
shoeshine.
Exactly. Since I was seeing no shoe-shining even with compression on (ie |
somewhere between 11 and 22 MB/sec) this indicates that the drive is
matching the speed to the incoming data. |
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Curious George
Guest
|
| Posted:
Tue Oct 18, 2005 7:26 am Post subject:
Re: DLT or LTO or AIT for new tape drive? |
|
|
On Mon, 17 Oct 2005 18:00:25 -0400, Steve Cousins
<steve.cousins@maine.edu> wrote:
| Quote: |
Curious George wrote:
But that still does not mean compression capabilities 'indicate' that
the drive 'has the ability to slow up automagically' when there are
throughput problems (i.e. variable speed).
Yes. I never meant to imply that compression indicates variable tape
speed. What I said was:
"Since I do set hardware compression on with setdensity, this makes
another case that it has variable speed capabilities since with
compression, it wants up to 22 MB/sec."
|
That quote isn't helping you
| Quote: | I agree, though, that compression can make it easier for there to be a
scenario where demand exceeds throughput, and _if_ the tape has the
ability to slow it will. But if it doesn't it won't; it'll just
shoeshine.
Exactly. Since I was seeing no shoe-shining even with compression on (ie
somewhere between 11 and 22 MB/sec) this indicates that the drive is
matching the speed to the incoming data.
|
Problem is I have seen shoeshining in similar backups (out of the
box), & haven't noticed terribly good compensation if at all.
Rather than trying to troubleshoot an old scenario (which doesn't
happen anymore after an Gb upgrade) I simply acknowledge the drives
you mentioned that could perform that way do, even if the feature
isn't as widely & accurately publicized as perhaps it should. |
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Lady Margaret Thatcher
Guest
|
| Posted:
Tue Oct 18, 2005 7:26 am Post subject:
Re: DLT or LTO or AIT for new tape drive? |
|
|
On Mon, 17 Oct 2005 20:44:05 GMT, Curious George <cg@email.net> wrote:
| Quote: | On Mon, 17 Oct 2005 10:58:08 -0400, Steve Cousins
steve.cousins@maine.edu> wrote:
Since I do set hardware compression on with setdensity, this makes
But that still does not mean compression capabilities 'indicate' that
the drive 'has the ability to slow up automagically' when there are
throughput problems (i.e. variable speed).
I agree, though, that compression can make it easier for there to be a
scenario where demand exceeds throughput, and _if_ the tape has the
ability to slow it will. But if it doesn't it won't; it'll just
shoeshine.
|
Curious George,
Your last paragraph has defined my question exactly. (Ignoring
compression). Which technologies or vendors do in fact adjust tape
speed? Exabyte claims that their VXA drives are the only ones that do
in fact adjust tape speed.
I've seen terms like "adjustable" or "dynamic" on other vendors'
sites, but it is possible that these vendors are conflating the change
in incoming data rate as a result of changes in compression ratio.
Or, it's possible that some drives don't do compression if the
incoming data isn't arriving fast enough. It's not possible to tell
from the descriptions on the web sites.
--Lady Thatcher-- |
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Curious George
Guest
|
| Posted:
Tue Oct 18, 2005 7:26 am Post subject:
Re: DLT or LTO or AIT for new tape drive? |
|
|
On Mon, 17 Oct 2005 21:39:22 -0700, Lady Margaret Thatcher
<Was_at_10_Downing_Street@bad_for_the_UK.org> wrote:
| Quote: | On Mon, 17 Oct 2005 20:44:05 GMT, Curious George <cg@email.net> wrote:
On Mon, 17 Oct 2005 10:58:08 -0400, Steve Cousins
steve.cousins@maine.edu> wrote:
Since I do set hardware compression on with setdensity, this makes
But that still does not mean compression capabilities 'indicate' that
the drive 'has the ability to slow up automagically' when there are
throughput problems (i.e. variable speed).
I agree, though, that compression can make it easier for there to be a
scenario where demand exceeds throughput, and _if_ the tape has the
ability to slow it will. But if it doesn't it won't; it'll just
shoeshine.
Curious George,
Your last paragraph has defined my question exactly. (Ignoring
compression). Which technologies or vendors do in fact adjust tape
speed? Exabyte claims that their VXA drives are the only ones that do
in fact adjust tape speed.
|
That's dishonest. Others do as reported here by Steve Cousins.
Unless they mean the only "consumer tape drive." In which case it's
misleading but correct AFAIK.
| Quote: | I've seen terms like "adjustable" or "dynamic" on other vendors'
sites, but it is possible that these vendors are conflating the change
in incoming data rate as a result of changes in compression ratio.
|
Not everything is equally compressible. The compression algorithm
handles that in firmware or software outside of that other feature.
The other feature you are looking for is basically a drive not waiting
for a total and expected buffer underrun and slowing the tape to keep
the buffer filled. Two separate ideas. Multiple marketing names
| Quote: | Or, it's possible that some drives don't do compression if the
incoming data isn't arriving fast enough. It's not possible to tell
from the descriptions on the web sites.
--Lady Thatcher--
|
Some drives aren't capable of compression (rare & unusually bad/old)
or speed compensation (now common but not totally ubiquitous). Some
that are don't advertize the fact they do in the most clear way. The
short answer is basically all the DLT's & LTO's currently being made
or recently retired do this & are worth a look. |
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Lady Margaret Thatcher
Guest
|
| Posted:
Wed Oct 19, 2005 9:42 pm Post subject:
Re: DLT or LTO or AIT for new tape drive? |
|
|
On Tue, 18 Oct 2005 06:08:11 GMT, Curious George <cg@email.net> wrote:
| Quote: | On Mon, 17 Oct 2005 21:39:22 -0700, Lady Margaret Thatcher
Was_at_10_Downing_Street@bad_for_the_UK.org> wrote:
On Mon, 17 Oct 2005 20:44:05 GMT, Curious George <cg@email.net> wrote:
On Mon, 17 Oct 2005 10:58:08 -0400, Steve Cousins
steve.cousins@maine.edu> wrote:
Your last paragraph has defined my question exactly. (Ignoring
compression). Which technologies or vendors do in fact adjust tape
speed? Exabyte claims that their VXA drives are the only ones that do
in fact adjust tape speed.
That's dishonest. Others do as reported here by Steve Cousins.
Unless they mean the only "consumer tape drive." In which case it's
misleading but correct AFAIK.
|
Curious George,
I must say. You seem to be very knowledgeable about tape drives. Are
you a storage administrator for a large SAN or do you work for a drive
company?
Anyway, the comment above. Are you implying that VXA is not in the
same league as say LTO or DLT? Why? Quality? Performance?
Durability of the media?
| Quote: |
I've seen terms like "adjustable" or "dynamic" on other vendors'
sites, but it is possible that these vendors are conflating the change
in incoming data rate as a result of changes in compression ratio.
Not everything is equally compressible. The compression algorithm
handles that in firmware or software outside of that other feature.
The other feature you are looking for is basically a drive not waiting
for a total and expected buffer underrun and slowing the tape to keep
the buffer filled. Two separate ideas. Multiple marketing names
|
The two separate ideas are (1) compression and (2) variable tape
speed? Right?
| Quote: | Or, it's possible that some drives don't do compression if the
incoming data isn't arriving fast enough. It's not possible to tell
from the descriptions on the web sites.
--Lady Thatcher--
Some drives aren't capable of compression (rare & unusually bad/old)
or speed compensation (now common but not totally ubiquitous). Some
that are don't advertize the fact they do in the most clear way. The
short answer is basically all the DLT's & LTO's currently being made
or recently retired do this & are worth a look.
|
Got it. Sounds like you are pointing me to DLT and LTO, but not AIT,
and you're suggesting that VXA isn't as good as these two.
Obviously I will need to be concerned about price. Now, for my
"consumer" application backing up a TB+ of digital photo data, where I
won't be running the drive non-stop, would VXA be OK,
--thatcher-- |
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