Re: [Veritas-bu] Real World NBU Buffer settings Win2k3

2010-09-21 13:25:40
Subject: Re: [Veritas-bu] Real World NBU Buffer settings Win2k3
From: Ed Wilts <ewilts AT ewilts DOT org>
To: "WEAVER, Simon (external)" <simon.weaver AT astrium.eads DOT net>
Date: Tue, 21 Sep 2010 12:25:33 -0500
On Wed, Sep 15, 2010 at 12:59 PM, WEAVER, Simon (external) <simon.weaver AT astrium.eads DOT net> wrote:

Anyone got any real world experience on buffer settings:

Win2k3 San Media, connected to 2GB Fabric attached 8 LTO4 Drives.
Due to drive availability, Multiplexing onto one drive.

Uggh.   With LTO4 drives, your ideal situation would be ONE tape drive per 4Gbps HBA port if you're doing any sort of compression.  If you can get 3:1 compression, you need to get 360MB/sec into your tape drive.  With 2:1 compression, you'll have already over saturated a single LTO4 drive.

> Main problem: One volume (1,7tb in size) takes over 4 days to fully complete.

On a compressed volume (as seen in other postings in this thread), you also burn a large amount of CPU to uncompress the data.  With a standard file system backup, each file needs to be uncompressed by NTFS before NetBackup gets it.  You then compress it at the tape drive.  And you're obviously getting good compression or you wouldn't do this on the file system in the first place.  So get back to my original point of not being able to drive the tape drive fast enough.

You don't have just a buffer problem - it's actually the least of your problems.

From another posting of yours:

> Cannot understand how we can recover a system is 2 days, when it takes double to backup completely!

Recovery is typically longer than backup as well...

> Have also mixed with Multiplexing, and no joy!

Multiplexing makes backups go faster but recoveries go slower.  You need to focus on recoveries, not backups.  The fastest recovery (from tape) will come from a fast media server and with multiplexing turned off.  And turn off NTFS-based compression - to recover that data will mean either you restore to an uncompressed disk or the server is going to have to compress all that data again after it comes off of tape.


ewilts AT ewilts DOT org

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