Quantum SDLT 320 & AHA 2940UW Configuration Help Please

[Jellyman5264]

Hi
I was able to get a used Quantum SDLT 320 external drive and I would
appreciate some help with the configuration. I purchased a used AHA
2940UW to work with the drive. (I know that I should have bought a
better one, but that was all they had "used" at the store)
The problem that I have is that I do not have any idea what the correct

settings on the AHA-2940 should be. There are many settings in the SCSI

Select utility.

I am using the terminator that came with the drive and a SCSI III cable



The tape does back up, but very slow and seems to write for a second or

two, pauses then writes again. (almost in small bursts


The last backup (using Windows Backup) that was attempted indicated
that it would take over 3 hours to back up 40 Gb ?


I have used a cleaning cartridge on the drive and using new media


Quantum tech support was little help..saying to call Adaptec who will
not even accept e-mails as the product is out of warranty ???


Thanks for your help


Jellyman

 

[Mike Tomlinson]

You might get more knowledgeable responses from comp.periphs.scsi, so
I've taken the liberty of crossposting there.

I was able to get a used Quantum SDLT 320 external drive and I would
appreciate some help with the configuration. I purchased a used AHA
2940UW to work with the drive. (I know that I should have bought a
better one, but that was all they had "used" at the store)

Essentially, you're using a 320Mbps device with a 40Mbps adapter and
wondering why it doesn't work well?

The problem that I have is that I do not have any idea what the correct

settings on the AHA-2940 should be. There are many settings in the SCSI

Select utility.

I'd just select adapter defaults then save the settings.

The tape does back up, but very slow and seems to write for a second or
two, pauses then writes again. (almost in small bursts

It sounds to me as if the tape isn't streaming, but is "shoeshining"
(constantly stopping and rewinding to allow writing to recommence after
the last block of data written.) Some more recent tape drives are
supposed to be able to vary the tape speed to allow streaming to occur,
but I suspect that the 2940UW isn't fast enough to allow that to happen
in your case; there is a minimum required write speed for the tape
drive to stream.

To help you compare, I use an LTO-3 (400/800GB) drive on a 29160 which
is quick enough to allow the tape drive to stream. It regularly backs
up 104861MB on four filesystems in 1hr 16min, i.e. 1380MB/minute. This
compares well with the theoretical speed of the SCSI connection: 160Mbps
= 20 MBps = 1200MB/minute.

 

[Steve Cousins]

Essentially, you're using a 320Mbps device with a 40Mbps adapter and
wondering why it doesn't work well?

Not really. The device has a I/O rate of 16 MB/sec and the SCSI card
can do 40 MB/sec so it should be fine as long as there isn't another
device on the SCSI chain that is doing a lot of I/O at the same time.
Presumably only the SDLT drive is on the bus.

I'd just select adapter defaults then save the settings.

I think so too.

It sounds to me as if the tape isn't streaming, but is "shoeshining"
(constantly stopping and rewinding to allow writing to recommence after
the last block of data written.) Some more recent tape drives are
supposed to be able to vary the tape speed to allow streaming to occur,
but I suspect that the 2940UW isn't fast enough to allow that to happen
in your case; there is a minimum required write speed for the tape
drive to stream.

The SDLT 320 can vary the rate too. It has a lower limit (can't remember
off the top of my head) so you still need to be able to stream to the
drive at probably at least 8-10 MB/sec.

Other factors:

1. How fast can the data be read from the drive being backed up?
2. Block size is important. Using the default value with tar on a
Linux system makes it very slow. I use a block size of 512KB with SDLT
and LTO3 drives with good results.
3. Cables and terminator.
4. If compression is on, you need to stream to the tape drive at
roughly (8 MB/sec * Compression ratio) where 8 MB/sec is my estimate of
the minimum rate that drive can slow down to.

To help you compare, I use an LTO-3 (400/800GB) drive on a 29160 which
is quick enough to allow the tape drive to stream. It regularly backs
up 104861MB on four filesystems in 1hr 16min, i.e. 1380MB/minute. This
compares well with the theoretical speed of the SCSI connection: 160Mbps
= 20 MBps = 1200MB/minute.

This is some weird coincidence since the numbers aren't correct. The
LTO-3 streams at 80MB/sec so you can theoretically back up 4.8 GB/min.
The 29160 has 160 MBps (Bytes not bits) channels but the limiting factor
is the drives (both the tape drive and the source drive), not the
channel speed. You are backing up at about 23 MB/sec which is a bit
more than a quarter of the potential speed of the drive. Probably you
are being limited by your source drive speed or a block size issue.

 

[Jellyman5264]

Thank you Steve

Although I am still somewhat confused about the whole affair. This is
my 1st venture into the world of SCSI.

After trying every combination that I could find, the settings on the
2940UW have been set back to default. Unfortunately the result seems to
be the same.

There is only 1 device on the chain.... I believe that I have the
correct cables & termination.

I would be happy to post all the settings from SCSI Select if you would
be kind enough to address them...

After reading Mike's comments, I was about to look into purchasing a
AHA-29160 at my local clone store..

However,

If you are suggesting that the 2940UW would be adequate with correct
settings, then I will not drop $300.00 on an AHA-29160.

As mentioned before, I am using Windows Backup as I can not justify
spending a few hundred $$ on Backup Exec just for home stuff...is there
a way to tweak Windows Backup to adjust the block size ? or is it a
hardware thing ?

How would I vary the rate on the SDLT 320 ?

Can you recommend some sort of S/W that would be free and do the trick
?

In a somewhat humorous note, I found a Belkin Firewire/SCSI adapter
that will back up the same amount of date in 2 hours ?

Best regards

Bill

 

[Mike Tomlinson]

4. If compression is on, you need to stream to the tape drive at
roughly (8 MB/sec * Compression ratio) where 8 MB/sec is my estimate of
the minimum rate that drive can slow down to.

It occurred to me that software compression may also be enabled in the
OP's host machine backup utility, which might slow down the machine
enough (depending on its processor) to affect the data rate going out to
the tape drive.

This is some weird coincidence since the numbers aren't correct.

You're right, many apologies. I'm used to dealing with serial protocols
and forgot that SCSI is parallel!

The
LTO-3 streams at 80MB/sec so you can theoretically back up 4.8 GB/min.
The 29160 has 160 MBps (Bytes not bits) channels but the limiting factor
is the drives (both the tape drive and the source drive), not the
channel speed. You are backing up at about 23 MB/sec

I'm using the *nix dump utility, which outputs an estimate of the backup
speed as it progresses. This can display up to 29,000KBps, which
tallies with the 23MB/sec you quote.

which is a bit
more than a quarter of the potential speed of the drive. Probably you
are being limited by your source drive speed or a block size issue.

It's probably the source drives. One is a very old 4GB 50 pin SCSI
drive, the other three are IDE devices. The 29160 is also in a 32-bit
PCI slot.

 

[Steve Cousins]

After trying every combination that I could find, the settings on the
2940UW have been set back to default. Unfortunately the result seems to
be the same.

There is only 1 device on the chain.... I believe that I have the
correct cables & termination.

You'll need to find out what rate the drive is negotiating with the SCSI
controller. I don't have any Windows machines that have any SCSI
controllers so I'm afraid I can't help on figuring that out. I don't
believe SCSISelect shows this. Probably there is a something in the
Administrative Tools control panel -> Computer Management that will tell
you this information. Or possibly in the Event Viewer. I'm sure
someone on this list knows how to do this in Windows. (?)

If you have a Linux boot CD you could try booting it up and it will show
you what rate it is negotiated at. I have a 2940UW with a Seagate drive
attached and it shows it negotiating at 40 MB/sec.

A tool that I have read about but never used is scsitool.exe at
http://www.nu2.nu/scsitool/.

I would be happy to post all the settings from SCSI Select if you would
be kind enough to address them...

If it is set to the defaults just make sure it shows 40 MB/sec as the
maximum rate.

After reading Mike's comments, I was about to look into purchasing a
AHA-29160 at my local clone store..

However,

If you are suggesting that the 2940UW would be adequate with correct
settings, then I will not drop $300.00 on an AHA-29160.

Yes. The 29160 is overkill.

As mentioned before, I am using Windows Backup as I can not justify
spending a few hundred $$ on Backup Exec just for home stuff...is there
a way to tweak Windows Backup to adjust the block size ? or is it a
hardware thing ?

How would I vary the rate on the SDLT 320 ?

It is up to your OS and Backup program. Again, I don't know how to do
this in Windows. Someone else?

Can you recommend some sort of S/W that would be free and do the trick
?

With UNIX/Linux, mt and tar work great. I don't know about windows
programs for this.

In a somewhat humorous note, I found a Belkin Firewire/SCSI adapter
that will back up the same amount of date in 2 hours ?

The big unanswered question right now is what drives are you backing
up? It is quite possible that these are the problem. Let us know and
this may point to the real problem. If they are old and slow, then even
this Belkin adapter won't help.

Good luck,

Steve

 

[Folkert Rienstra]

It occurred to me that software compression may also be enabled in the
OP's host machine backup utility, which might slow down the machine
enough (depending on its processor) to affect the data rate going out to
the tape drive.


You're right, many apologies. I'm used to dealing with serial protocols
and forgot that SCSI is parallel!


I'm using the *nix dump utility, which outputs an estimate of the backup
speed as it progresses. This can display up to 29,000KBps, which
tallies with the 23MB/sec you quote.


It's probably the source drives.

One is a very old 4GB 50 pin SCSI

The 23MB/s is rather obviously not from that one.

drive, the other three are IDE devices.

The 29160 is also in a 32-bit PCI slot.

Which is totally acceptable.

 

[Folkert Rienstra]

Not really. The device has a I/O rate of 16 MB/sec

32MB/s under ideal conditions according to Quantum specs.
And you're comparing different rates, the drive is Ultra2 at 80MB/s.
However, some desktop versions may be 40MB/s as well, limited
by a SE-UW or HVD-UW external SCSI interface connection.

and the SCSI card can do 40 MB/sec

30-35MB/s, actually.
40MB/s is the bus clockrate converted to MB/s.

so it should be fine as long as there isn't another device on
the SCSI chain that is doing a lot of I/O at the same time.
Yes.

Presumably only the SDLT drive is on the bus.

Default should be fine.

I think so too.

The SDLT 320 can vary the rate too.

Quantum make no mention of it (that I can find).
They do mention SDLT220 compatability mode tho (11MB/s).

It has a lower limit (can't remember off the top of my head)

If there is than it must be in the general DLT specs.
Quantum only specify one (fixed) tapespeed.

What I *am* able to find is adaptive caching, adaptive block size and
adaptive compression to keep the drive streaming as much as possible.

so you still need to be able to stream to the
drive at probably at least 8-10 MB/sec

Other factors:

1. How fast can the data be read from the drive being backed up?
2. Block size is important. Using the default value with tar on a
Linux system makes it very slow. I use a block size of 512KB with SDLT
and LTO3 drives with good results.
http://downloads.quantum.com/sdlt320/handbook.pdf

3. Cables and terminator.

4. If compression is on, you need to stream to the tape drive at
roughly (8 MB/sec * Compression ratio) where 8 MB/sec is my estimate of
the minimum rate that drive can slow down to.

I would make that 16 or 11.

 

[Folkert Rienstra]

You'll need to find out what rate the drive is negotiating with the SCSI
controller. I don't have any Windows machines that have any SCSI
controllers so I'm afraid I can't help on figuring that out.

I don't believe SCSISelect shows this.

No, it doesn't. SCSI BIOS at POST does from some newer version on.
If he has a very old BIOS he can update that to v3.10

Probably there is a something in the Administrative Tools control
panel -> Computer Management that will tell you this information.
Nope.

Or possibly in the Event Viewer.
I'm sure someone on this list knows how to do this in Windows. (?)

I don't think Windows drivers transfer this info at all.

If you have a Linux boot CD you could try booting it up and it will show
you what rate it is negotiated at. I have a 2940UW with a Seagate drive
attached and it shows it negotiating at 40 MB/sec.

A tool that I have read about but never used is scsitool.exe at
http://www.nu2.nu/scsitool/.

Doesn't either.

If it is set to the defaults just make sure it shows 40 MB/sec as the
maximum rate.

It should be unless this is some weird OEM with different defaults.

Yes. The 29160 is overkill.

Very. Especially if he has the UW version of the drive.

It is up to your OS and Backup program. Again, I don't know how to do
this in Windows. Someone else?


With UNIX/Linux, mt and tar work great. I don't know about windows
programs for this.


The big unanswered question right now is what drives are you backing
up? It is quite possible that these are the problem. Let us know and
this may point to the real problem.

If they are old and slow, then even this Belkin adapter won't help.

And has to be FW800 to be faster than the 2940UW.

 

[Steve Cousins]

32MB/s under ideal conditions according to Quantum specs.
And you're comparing different rates, the drive is Ultra2 at 80MB/s.
However, some desktop versions may be 40MB/s as well, limited
by a SE-UW or HVD-UW external SCSI interface connection.

32 MB/s is with compression (their fairly optimistic guess of 2:1
compression which of course depends on the data). 16 MB/s is native.

30-35MB/s, actually.
40MB/s is the bus clockrate converted to MB/s.

Got it.

Quantum make no mention of it (that I can find).
They do mention SDLT220 compatability mode tho (11MB/s).

I know. This is bizarre. It is a great feature but they don't say much
about it. Do a Google Groups search with "SDLT DDRA" and you will find
one thread that I was involved in that discussed this in (too much)
detail.

 

[Steve Cousins]

Quantum make no mention of it (that I can find).
They do mention SDLT220 compatability mode tho (11MB/s).

Here is a paper I found that talks about SDLT 320 vs. LTO 1 as far as
their variable rate recording compares:

http://www.gstinc.com/resources/file/DigitalSpeedMatchingWhitepaper.pdf

Steve

 

[Jellyman5264]

Thanks for all the info

I did a bit of digging myself and figured out that the AHA 2940UW will
only operate in SE mode


With the terminator I have, "a red light means the system is operating
in SE mode. Your performance will be poor at best when running in SE
mode."

Perhaps this is causing part / most of the problem.

Do you agree or am I off base ( i know very little of this)

As I mentioned when I started this thread, I am using the Backup that
comes with XP and have no control over recording rates.

The defaults have been set on the card and a great deal of "shoe
shining" is happening.

If one of you knows how to adjust anything (drive or O/S) that will
make the drive work well, I would appreciate it very much

Best regards

 

[Steve Cousins]

Thanks for all the info

I did a bit of digging myself and figured out that the AHA 2940UW will
only operate in SE mode

With the terminator I have, "a red light means the system is operating
in SE mode. Your performance will be poor at best when running in SE
mode."

Perhaps this is causing part / most of the problem.

Do you agree or am I off base ( i know very little of this)

As I understand it, the card is not an LVD card so it will always show
up as SE. You can still get the full 40 MB/sec (or 30 to 35 as Folkert
says) in SE mode though.

As I mentioned when I started this thread, I am using the Backup that
comes with XP and have no control over recording rates.

There may be a registry setting.

The defaults have been set on the card and a great deal of "shoe
shining" is happening.

If one of you knows how to adjust anything (drive or O/S) that will
make the drive work well, I would appreciate it very much

Again, you need to tell us what the drives are that you are backing up.
And how they are connected. Ideally you would get a benchmarking
program (iobench comes to mind) to see how fast your drives are too and
give this information to us. Without this information we can't really
narrow down the problem.

 

[Jellyman5264]

Sorry about that....The drives that are to be backed up are regular 40
Gb IDE / ATA drives that i have had around for a while.

Bill

 

[Folkert Rienstra]

32 MB/s is with compression (their fairly optimistic guess of 2:1 compression

which of course depends on the data).

Unless 2:1 is an average.

16 MB/s is native.

Native is on the tape side.
What matters is what has to be supplied on the interface side to keep
the drive streaming. Apparently that is between 16 and 32MB/s.
And with the adaptive buffering we are talking about an average here.

As long as the system can keep the buffer from underrunning it doesn't need
to be a steady 16MB/s (or more). As long as the average for a period that it
takes to write the buffer to tape is 16MB/s (or more) it should be OK.
This does of course mean that the system has to have the ability to tranfer
faster than that 16MB/s to compensate for the times that it is slower.
And with random access data it has to be a lot faster than that too to
compensate for the inescapably occurring latencies in the data stream.

Got it.


I know. This is bizarre.

It is a great feature but they don't say much about it.

As in nonexistent.

Well apparently that is the name that they (or someone) came up with for
all the adaptive features (caching, block size and compression) combined.

Do a Google Groups search with "SDLT DDRA" and you will find one
thread that I was involved in that discussed this in (too much) detail.

But nothing much came out of it other than the usual speculation.

 

[Folkert Rienstra]

Here is a paper I found that talks about SDLT 320 vs. LTO 1 as far as
their variable rate recording compares:

http://www.gstinc.com/resources/file/DigitalSpeedMatchingWhitepaper.pdf

Would be interesting to know how much tape each used to accomplish those speed results.
In other words, what was the useable capacity of the cartridges with that particular test
use of both systems.

 

[Folkert Rienstra]

Thanks for all the info

I did a bit of digging myself and figured out that the AHA 2940UW will
only operate in SE mode.

Since it is a SE SCSI controller you can stake your life on that.

With the terminator I have, "a red light means the system is operating
in SE mode.

Yeah, how about that eh.

Your performance will be poor at best when running in SE mode."
Nonsense.


Perhaps this is causing part / most of the problem.

Nope. That drive is also sold in that type of configuration.

Do you agree or am I off base ( i know very little of this)

It shows.

As I mentioned when I started this thread, I am using the Backup that
comes with XP and have no control over recording rates.

The defaults have been set on the card and a great deal of "shoe
shining" is happening.

If one of you knows how to adjust anything (drive or O/S) that will
make the drive work well, I would appreciate it very much

Best regards

Make image backups (instead of file backups).
RTFM (the one that I mentioned in the other post).

 

[Folkert Rienstra]

Sorry about that....

No you don't.

The drives that are to be backed up are regular 40
Gb IDE / ATA drives that i have had around for a while.

You are not going to tell us what they are, are you.
You are going to maximise this thread by deliberately being as unhelpful
as you can. See if you can draw blood. See if you can have someone loose
his patience with you so you can complain of how unhelpful this group is.
Never follow-up on instructions but come up with other questions instead.
Draw comments about topposting and how topposters never appear to read.
You demand spoonfeeding, who the hell are we to ask you questions back, right?

Ehm, did I miss something?

 

[Jellyman5264]

Folkert,

I am terribly sorry if I have offended you with my lack of knowledge
about this topic or posting in this group.

It never occurred to me that the actual drive type would have any
bearing on the tape doing this "shoe-shining"

I can tell you that I have tried to backup the various IDE drives
(Seagate & IBM / 40Gb ~ 9 ms ) in my system, all with the same result.

Although I appreciate your assistance, I find it quite rude of you to
chastise me in this way. I can assure you that I am not doing this to
"draw blood" oar anything of the sort.
I simply am looking for information from people who know more about
this than I do.

If you have no patience for new users such as myself, please have the
fortitude to ignore this thread.

Bill

 

[Steve Cousins]

It never occurred to me that the actual drive type would have any
bearing on the tape doing this "shoe-shining"

It is part of the equation. The tape drive can only work as fast as the
data can come in. The data can come in only as fast as the disks can be
read from, and everything in between.

I can tell you that I have tried to backup the various IDE drives
(Seagate & IBM / 40Gb ~ 9 ms ) in my system, all with the same result.

If you can give a model number this would help since there are different
generations of 40 GB drives which have different performance.