Re: [Veritas-bu] Multiplexing on VTLs

On Wed, Apr 30, 2008 at 6:36 PM, Mike Sparkes <Mike.Sparkes AT quantum DOT com> wrote:

Multiplexing mixes streams of data from multiple sources into one stream to the storage device. A de-duplication product on that storage device will be breaking up the stream into blocks and looking for duplicate blocks. Let us assume that three backups are being multiplexed and that no data changed since the previous backup. It is unlikely that the data will mix together again at the same rate in the same ratios to create the same blocks and so they will be treated as unique and stored in full.

I disagree. Multiplexing doesn't mix up the blocks coming from each server. You may see things like block 1 and 2 from server 1 followed by blocks 1, 2, and 3 from server 2, but if block 2 from server 1 is the same as block 3 from server 2, it will de-dupe. It doesn't matter what the speed is today versus yesterday - you're not de-duping the tape but you're de-duping the blocks.

Duplication typically is not done by files - it's done by blocks, and that isn't changing with multiplexing.

.../Ed

Mike Sparkes

From: Ed Wilts [mailto:ewilts AT ewilts DOT org]
Sent: Wednesday, April 30, 2008 4:12 PM
To: Mike Sparkes

Cc: veritas-bu AT mailman.eng.auburn DOT edu

Subject: Re: [Veritas-bu] Multiplexing on VTLs

On Wed, Apr 30, 2008 at 5:58 PM, Mike Sparkes <Mike.Sparkes AT quantum DOT com> wrote:

if you ever move
to de-duplication, the act of multiplexing your backups ruins the
ability to detect duplicate blocks. Your de-dupe ratio will be terrible.

I don't follow your logic here. Why would multiplexing affect the de-dupe ratio?

--
Ed Wilts, Mounds View, MN, USA
RHCE, BCFP, BCSD, SCSP
mailto:ewilts AT ewilts DOT org

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