ADSM-L

Re: [ADSM-L] Dedupe

2009-06-25 11:07:00
Subject: Re: [ADSM-L] Dedupe
From: Richard Rhodes <rrhodes AT FIRSTENERGYCORP DOT COM>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Thu, 25 Jun 2009 11:04:20 -0400
> I a dedup appliance, that is exactly what you don't have.  The dedup
> process guarantees that only one copy is kept of each unique block of
> that data.  If a given block of data is lost due to corruption or
> failure of the media, then potentially all of the copies of a certain
> file that contains that block of data will be lost.  The people who are
> designing these products, therefore, build their products to mitigate
> this potential loss by:

This is exactly what scares me about dedup - the unit of recovery.  For
our current (and foreseeable future) tape systems, the unit of loss
and recover is a TAPE.  With a VTL/dedup
it's a much larger unit which is hard to define, but could be up to the
entire appliance.  A software bug could potentially take out not
only a local appliance, but a replication target.

When DataDomain was here a few weeks ago, I asked them if they have
ever had a data loss event.  They quickly replied "NO".  I wish I
knew whether to believe them - vendors do NOT like to acknowledge
crashed systems.

Another question I asked - Why would I EVERY have to take your
system down?  Their reply what that it takes about 2hr to perform
a microcode load.  Other than that, it should never have to come down.
That then leads to a discussion of frequence of code releases and
how quickly one must upgrade. (I don't remember their answer)

There is a part of me that strongly wishes we had a VTL/dedup system,
but another part is very happy to be sitting out this round with all
the vendor consolidation and product changes.

( Note: I am a FIRM BELIEVER in the worse case scenario! )

Rick


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