Another compression Q on storageworks DAT72 ntbackup

[Davown]

Just another user trying to sort out why actual compression is half the level promised in HP marketing brochures:

I have an SBS 2003 HP Proliant G4p whatever server with internal HP Storageworks USB DAT72 tape drive.

I believe its model C7438A serial number HU10609W1Z (saw that somewhere but being internal makes it hard to verify).

It should have a 72GB capacity but is capping or crapping out at 43GB which is causing grief for my backup strategy.

Tape drive properties indicate capacity is 38GB and compression enabled is false.

HP website says to use their drivers rather than MS drivers. Server was using their driver hpdat.sys version 1.5.3.1 and is now using new version 1.5.3.2. I upgraded driver but to no avail.

NTbackup is set up to use hardware compression but everything indicates hardware compression is not happening.

I have also downloaded HP L&TT and tried to do the configure thing (set compression) but that test (I would call it a configuration change myself) failed.

I emailed this issue to HP online support two days ago and still waiting, waiting....

I have read through the forum on tape drives with compression problems and could not see an answer.

I am aware NTFS may already compress my files and that I should not expect 2:1 compression but I'll believe that when I see my hardware compression enabled and compression happening.

Not too excited about pulling my server apart to check DIP switches (could kill that IT salesman for selling me an internal drive!).

Is there an easier way to resolve this gremlin. Surely after 4 years and 4,000 forum questions on hardware comression HP have a comprehensive analysis on what is needed and a utility to KISS-fix it. It can't be that hard.

This is the fourth problem in lack of support on HP products I have suffered in as many months and its starting to seriously annoy me.
Davown

[Lewis Finch]

Hardware compression is enabled by default (you do not have to cahnge any dip switches) on this drive and should be used instead of software compression. If you are using NTFS and the files are already compressed then you are getting about what you should expect as far as capacity is concerned. If you ran the compression test in LTT what were the results?

[Davown]

Thanks Lewis;

Since yesterday's post, I have:
- done LTT compression test - passed.
- done LTT Test - Drive Config disable compression - passed
- done LTT Test - Drive Config ensable compression - failed
- pulled server apart and can find no DIPs
- pulled plug out of internal DAT72 drive and restarted it (power down in effect);
- DAT72 properties reported Compression Enabled - TRUE
At last I thought I was getting somewhere. Seemed DIPs or no DIPs my DAT72 was resetting to correct default position and compression was possible BUT:

Why does LTT compression enable fail?????

Then:
- I started ntbackup but cancelled it after 30 minutes;
- checked DAT72 properties and they were stuffed again Compression Enabled - False

I get the impression ntbackup resets the compression to OFF after a backup stops. Hopefully this means that ntbackup sets compression to ON when it starts a backup but there is no way of checking this apart from emperical backup volumes.

Given my tapes are capping out at 40GB on a DAT72, the emperical result suggests compression is not happening, or as you allude, DAT72 hardware compression does little on an NTFS server.

So the conclusion I am reaching is that HP marketing blurb has misled both myself and the IT consultant who recommended the DAT72 for my 80GB server. It would appear the DAT72 is only going to provide 50% solution to my backup needs.

As Shania Twained: "That don't impressa me much"

[Richard Bickers]

Couple of thoughts.

It seems to me that NTbackup is turning hardware DC off not on. To my knowledge it doesn't leave it off by default. I just looked at the parameter list for NTbackup and it does say HC - hardware compression - pretty clearly so that's odd to me. I'd expect to see the LTT support ticket show DC enabled even after you cancel the backup. You could try some real quick backups with different options to see if you can get it to stay on.

You should be able to pull a support ticket with LTT immediately after the backup and it will tell you what the compression ratio has been since the tape was last loaded. If hardware compression was off you'll get 1:1, if it was on but trying to compress data that is already compressed then it will actually expand. You'll get something like 1:1.2. If it's compressing normally you'll get anywhere between 1.3:1 and 100:1 (empty DB).

We quote 2:1 as an average which is reasonably accurate for an average but obviously not what you'll get if the data is already compressed. I'm afraid everyone in the industry does that and we have to be consistent. There's a lot of confusion over compression ratios but what you get really boils down to what you're compressing and that could be anything.

One other thing you could try is to run the device performance test using 2:1 compressible data to the end of the tape. That will at least confirm you can get about the right amount of compressible data onto one tape. Won't help if you can't turn it on or have pre-compressed data though.

The LTT enable compression config (test) shouldn't fail. We'd like to know more about that. Could you please find the EventLog.ltt file in the LTT install directory to LTT.team@hp.com please? This is the LTT support mailbox.

I agree, this is a utility rather than a test but for the time being they're all together under one list. We'll fix that in a future release.

[Davown]

There are a number of log files - all relatively small so I attached them all. From what you write above there are signs this is a genuine problem worth investigating. I had almost given up on this issue, thinking the NTFS OS was the problem but could not understand why LTT utility was not enabling compression. Now your comment that ntbackup should not leave compression disabled gives me hope there remains a genuine problem and hope there must be a remedy.

Not sure where the LTT support ticket is but I will look for it in LTT on Monday. Being in Oz, there is a bit of a time differential in play here.

Glad to have your assistance and happy to work with you towards resolving this issue. Hopefully the attached logs tell you something but from my experience of troubleshooting PCs they rarely do.
Davown

[Richard Bickers]

We've got a FAQ for LTT which might be a handy reference. See www.hp.com/support/lttfaq and look in the contents for 'How do I generate a support ticket?'. The examples are LTO based but the same steps will work fine for a DAT72. You should be able to find the compression ratio OK. Remember that the counters are reset when the tape is loaded so you may need to do that each time if you're experimenting.

I assume your attachments went to the LTT support mailbox so I've asked them to look out for them. Hopefully you'll get some communication w.r.t. finding out why LTT can't set compression on in your drive. I'd like to get to the bottom of that one.

That may be a different issue to what's going on with NTbackup. That's a mystery all by itself. I know people use NTbackup successfuly with our drives so there's something amiss here.

It would be worth checking your file system settings to see if you've already got compressed files. I've not seen anything in the documentation but it's widely known that trying to re-compress data that's already compressed can lead to expansion (there's a little overhead with compression that is *usually* offset by the final size reduction) so it may be that NTbackup automatically turns of hardware compression if it knows the files are already compressed - whatever you set your parameters to. That's just a guess, mind, but it does fit the symptoms.

[Davown]

Okay, found the support ticket info and emailed that to LTT.team@hp.com as I did for logs.

The support ticket indicates that compression is disabled but does not id why. Perhaps it's ntbackup causing this problem, or perhaps another.....

I would be surprised if its another application interfering with DAT72 comression settings as our server is relatively new (6 months old) and I have a preference to minimise conflicts.

From my knowledge, compression has never worked on our server although this only became obvious about 3 months ago when our backups started to exceed 36GB.

Davown

[Predrag Kalabic]

I have a same problem with my DAT72 (internal SCSI). I use Windows 2003 with NTbackup, and the problem is that NTbackup doesn't use HC.
When I test DAT72 with LTT, it pass all test (2:1 ,3:1 compression) but I get warning massage that last backup was at 1:1 compression. Could it bee NTbackup problem, or can I do something with DAT72?

Predrag

[AstonT]

Hello, We have the same issue.
Using SBS2003 and HP Storageworks DAT72 USB internal drive.
I have had a backup exceed 36Gb but only just. Could it be that NTBACKUP is actually trying to backup to DDS4 media and not DAT72? DDS4 media is 20/40Gb.

Did you ever resolve your issues?

[Alan Mason]

Ever get a resolution? I have just upgraded a server from SBS 2000 to SBS 2003 and now I cannot get a full backup to the DAT 72. It always stops at around 36GB. I have tested with both NTbackup and Yosemite Backup. Both appear to fail to enable compression, but HP LTT passes its compression test. Interestingly, when I look at the drive through HP LTT it indicates that compression is enabled, but when I look at the device properties in device manager it shows as compression enabled = FALSE.