Slow backup with DSS and Quantum SuperLoader 3

Hi,

I've just set up a backup solution based on Open-e DSS connected to a Quantum SuperLoad 3.

I've set up the snapshots and backup pool and tasks.. everything seems to be working fine, except that the writing tho the tape is very very slow.


Mail01 Tape Append 25.14GB/(n/a)
first written:2008-06-27 15:49:57
last written:2008-06-27 18:38:24

What could be causing such a lowspeed, is there something I can change in Open-e to increase the writing speed.

Other think I noticed, is that the tape is not "Writing" most of the time.. it alternates between "writing" for a couple of seconds and then "idle" for many many seconds.

I don't think this could be related with bad SCSI connection..

Anyone with a similar issue?
Thanks!

Check you cache,
what raid controller are you using ?

Hi,

The raid controler is a 3ware Inc 9650SE SATA-II RAID and the autoloder is connected to an Adaptec ASC-29320ALP U320.

I believe you're talking about the controler settings, as I can't see any cache settings on DSS. I'll take a look at the 3DM interface when I get back to office.

You need to enable cache in the Adaptec controller not in 3ware.

Hi,

I thought it was the 3Ware raid controller that was not feeding data fast enought to the tape library. I enabled write cache in 3ware and backups to a virtual tape device become much faster, do not know how much faster but at least 2x.

However the backups to the tape library are still very slow.. the last test took 10hours to backup 70GB.

I took a look at the adaptec cli interface in DSS (Raid Tools menu) but didn't find a way to change the cache settings. the 'controllers list' doesn't list any controllers.

any tips on how to do this? is it some DSS setting, or is it directly in the controller card?
didn't find anything relevant on the controller BIOS either...

I'm still have no clue about this issue

The LTO2 max theoretical speed is about 40MB/s, right?
What speeds are you guys getting with a similar setup?

I'm getting about 2MB/s

I'm trying to ajust the said cache on the adaptec controler. have been looking for module options, etc so far no solutions

I'm tempted to try to boot with a liveCD to override dss, but I wanted to fix the problem within dss. Any more tips

Thanks

Hello HangaS,

Have you been able to make any progress with locating a root cause and/or a bottleneck?

Did you try to isolate the problem by taking some systematic approach, e.g. checking SCSI bus termination, trying another tape drive, verifying your SuperLoader performance on a different system, etc.?

Frankly speaking it reminds me a tape drive shoe shining effect usually caused by insufficient data amount provided by the IO pipe. If you don't stream data to the drive it stops and before writing again it needs to reposition the tape. However this should not take "many many" seconds... unless you stop streaming data for "many" seconds.

Piotr

HI Piotr,

No, unfortunatly I'm still having this problem. Altough I have checked SCSI terminations and cabling and everything looked ok I still have the problem.

I didn't tried the more dramatic aproaches of tried different harware as this is the only U320 scsi adapter/cable/tape that I have.
But I'm suspecting that it can related to SCSI HW or controller settings.

I left an automatic backup scheduled for the weekend and it didn't run at all because the tape was not found. When I checked the tape drive, it was missing in the tape devices.

It only got back to normal with a reboot. Well not quite.. now I have a runnnig backup task that I can't remove or stop :|

Hi,

Problem Solved!

I contacted open-e support, and they still could provide me a direct anwser, they also refered to some 'cache' setting in the Adaptec controller, and there is none.

However they qouted some part of the Adaptec user manual I didn't find relevant ate first but turned out to be the solution.

I forced the SCSI negotation to only 40MB/s non Wide as I guessed it would be more tolerant. The LTO2 speed is no bigger then 40MB/s anyway.

With this setting the tape is now writing more then 90% of the time.

A previous backup took 10h for 75GB. I now made a couple of backups of 150MB in 3h! A greater improvement!

I hope this could be of help to anyone in the future.

Hi,

can you give me some advice where to change the settings of the adaptec controller. I do not find any menu/page where to do it. All I have found is the web administration of the 3ware raid controller.

Thanks.