How can I speedup our backup

[Lothar Krueler]

Hi there,
regarding to "DLT speeds and multiple drives" I've got another question:
We use a library with 2 DLT 7000 drives, each drive is connectted to one L-2000 Server (Service Guard Cluster).
Backup-software ist OB II 3.0 on a third (D2070) Server. The L-2000 servers a both (Service Guard Cluster) connected (each alternately over 2 SCSI controllers) to one Autoraid 12H. The 12H is running mostly in raid level 0/1.
My Problem is, that in most cases data doesn't come quick enough to the DLTs. In the best case i get 22GB an hour (per drive and server). In worst case the DLTs leave streaming mode. Online-backup ist not possible.

We don't use Online JFS yet. Is it possible to use mirror copies on the autoraid with online jfs for backing up with short downtime?
Has anyone good suggestions ?

Thanks in advance
Lothar

[Paul R. Dittrich]

I think you are limited by the internal SCSI bus speeds. I don't think Online JFS will buy you much, if any, extra speed in this case.

[Stefan Farrelly]

On most of our large HP servers we use a 2nd mirror copy, then stop or freeze our applications, lvsplit the 2nd mirror, then restart the apps, then backup raw from the split mirror copy during the day, no problems. This way your backup speed isnt important as the data is preserved in the split copy and you application is back up or unfrozen as soon as the mirror is split, which should only take 5 mins. Other options are JFS snapshots, similar to a 2nd mirror copy, but more complicated to setup.

[Lothar Krueler]

Thanks Paul, Thanks Stefan,

Paul, of course you're right. My fault, I think online jfs allows to backup online but needs additional space for journaling. So the backup itself wouldn't go faster, but the applications could keep on running.

Stefan,
I thougt of backing up a mirror copy (while I read your reply to "DLT speeds ..." . My question now is : Is it possible/senseful to use mirrorcopies on the autoraid, and if : how can i do this ? Will the application/system slow down with the additional mirror ?
Should the mirror be part of the autoraid or better a additional normal drive?

Lothar

[Volker Borowski]

Lothar,

Online JFS has a SNAPSHOT-mount feature, that would do esp. what you want.

For an extra mirror copy you would need the same amount of space. For snapshots, your space-needs depend on the io-activity. So if your application just has a few writes, you will need less disks by going by snapshots.

I am not quite sure, but I think it works like this:
- Snapshotmount takes timestamp of FS to be mounted.
- If access to diskblock on snapshotmounted FS shows timestamp newer than snapshotmount, read data from log instead from real disk.

So if you have just a few writes, you will only need a small logging area.

Do not know if this helps.
Volker

[A. Clay Stephenson · Accepted solution]

Hi Lothar,

Your problem is twofold - first how to get as much performance as possible from your 12H and secondly how to back it up.

One of my configurations is very much like the one you describe. First the internal SE-SCSI buses are not much of a limitation because there are four of them. It appears that you are not striping across both external 12H controllers and that is one of the real keys to good performance. Each volume group should be made up of 2 LUN's with primary path X (alternate Y) on one of the LUN's and primary path Y (alternate X) on the other. Each logical volume in the voulme group should then stripe across both LUN's. I've found 64K stripe to be the optimum for vxfs. It's a little tricky to do a vgexport like this in an MC/SG environment. You need to not do a -s vgexport/vgimport but rather a vgimport using explicit paths. You then do a vgchange -c y after the vgimport to the 2nd server.

The idea is that each logical volume will fully utilize both controllers all the time.
You also indicated that most of your 12H storage is in 0/1 mode; that is very good and I would suggest that you leave as much space as possible uncofigured.

Rather than mirroring in an AutoRAID environment, use the OnlineJFS snapshot filesystem mount. The size of the snapshot buffer can be quite small (~5-15% depending on activity and the length of the backup.).
The snapshot operation itself requires only a few seconds and you do not see the big i/o hit when resyncing a mirror. One thing that I would suggest is that you mirror the snapshot buffer and this logical volume should be on a seperate disk pair.

I can say that backing up like this I have no difficulty streaming a pair of DLT7000's but speed is really not an issue because I'm backing up a snapshot.

Food for thought, Clay

[Lothar Krueler]

Thank you all,
"Food for thoughts" - i think so, too.

:-)) Lothar