Re: [Veritas-bu] LTO4 Performance With Exchange 2003 IS Poor

On Tue, Apr 7, 2009 at 8:12 AM, WEAVER, Simon (external) <simon.weaver AT astrium.eads DOT net> wrote:

Environment:
NBU 5.1 MP5 Master Plus many SAN SSO Media Servers Win2k3 SP2
Problem: Mail Backups of Information Store using LTO4 SL500 are taking 4 1/2 hours extra to backup compared to LTO3.

If the tape drives were not your bottleneck before - i.e. you were continually driving them at least 80MB/sec, then upgrading to LTO-4 will likely slow your backups down. By my calculations, you weren't bottlenecked at the tape drives. You were taking 4 hours for 1TB of data. That's a total of 69MB/sec. If you were doing that to 3 drives, you were only averaging 23MB/sec per drive.

LTO drives must stream. If you can't feed them data fast enough, you'll shoe-shine the drives with continuous start/stop fashion and performance will suck.

Same configuration is in place (ie: 3 streams to 3 different drives) and all part of the same fabric, apart from being in a different building.

An IBM LTO4 drive requires a MINIMUM of 30MB/sec. An HP LTO4 requires a MINIMUM of 40MB/sec. That's assuming no compression. If you're compressing with a 2:1 ratio, you'll need double that. They top out at 120MB/sec native and 240MB/sec with (2:1) compressed data.

So let's assume 2:1 compression on 3 streams going to an HP drive. You'll need to deliver 2*3*40MB/sec, or 240MB/sec at an absolute minimum. You can deliver up to 2*3*120 or 720MB/sec.

Since you were only averaging 23MB/sec per drive before, you've got a LONG way to go.

.../Ed

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

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