Re: [Veritas-bu] Destaging going slow

I know it does not help your configuration but destaging using SLPs from AdvancedDisk to LTO-4 we get 80-150 MB/s.

William D L Brown

From: veritas-bu-bounces AT mailman.eng.auburn DOT edu [mailto:veritas-bu-bounces AT mailman.eng.auburn DOT edu] On Behalf Of WALLEBROEK Bart
Sent: 24 June 2010 07:48
To: Ed Wilts
Cc: veritas-bu AT mailman.eng.auburn DOT edu
Subject: Re: [Veritas-bu] Destaging going slow

Ed,

Did you ever heard of NBU users who actually got heir speeds up to acceptable levels with DSSU ? I asked the same question this morning to NBU support but I’m pretty sure I already know what the answer will be.

Best Regards,

Bart WALLEBROEK

Backup Admin & Systems & Applications Management & Support Specialist
Enterprise Applications Delivery - Infrastructure Management

From: Ed Wilts [mailto:ewilts AT ewilts DOT org]
Sent: Wednesday, June 23, 2010 5:23 PM
To: WALLEBROEK Bart
Cc: veritas-bu AT mailman.eng.auburn DOT edu
Subject: Re: [Veritas-bu] Destaging going slow

On Wed, Jun 23, 2010 at 8:22 AM, WALLEBROEK Bart <Bart.WALLEBROEK AT swift DOT com> wrote:

We have a couple of windows (dedicated) Media Servers that act as NetBackup DSSU (Disk Staging Storage Unit) servers with each having from 4 to 16 TB of SAN disks. Backing up to them is no issue and goes up to the limit of the network connected clients. Destaging to tape (LTO4) however is slow (20 - 35 MB/sec).

We have been in contact with Symantec where they advised us to lower the fragment size, change the data buffers size and numbers but we seem to get stuck to the current speed. Backing up data from this DSSU disk to the tape drives goes up to physical tape speed limitation.

Does anyone have an idea where to look further to get to a reasonable speed ?

We currently are testing a Solaris DSSU server but we do not have numbers for that one.

We had this same issue escalated within Symantec and never did find the problem. We had no such restrictions writing from the media servers directly to the tape drives, even when going from the DSSU locations - i.e. dd went at full speed but a destage would go slow. reading the same file that dd read. We're also mostly Solaris but our Windows media server also saw the same performance degradation.

We're located close to the NBU developers so we had NetBackup engineers on site doing investigating and benchmarking. We duplicated the problems for them but they were unable to find any issues with the destaging code.

We eventually gave up on using DSSUs for the majority of our backups because the performance hit was unacceptable. If you find a solution, I'd really, really like to hear about it.

.../Ed

Ed Wilts, RHCE, BCFP, BCSD, SCSP, SCSE
ewilts AT ewilts DOT org

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