Veritas-bu

Re: [Veritas-bu] Reg: LTO3

2008-11-21 17:43:13
Subject: Re: [Veritas-bu] Reg: LTO3
From: Justin Piszcz <jpiszcz AT lucidpixels DOT com>
To: "Clausen, Matt R [EQ]" <Matthew.R.Clausen AT Embarq DOT com>
Date: Fri, 21 Nov 2008 17:32:41 -0500 (EST)

On Fri, 21 Nov 2008, Clausen, Matt R [EQ] wrote:

> Regarding the tape-drive based compression though, I think by default the 
> drive does not compress (actually I'm fairly positive this is the case). The 
> driver has to instruct the tape drive to enable hardware compression. In the 
> case of solaris, this is done based on which device you are physically 
> sending the backups to.
You're correct, in Linux, when NetBackup initializes the tape drives, it turns 
it on.  I did a lot of different testing myself with different backup vendors 
and noticed this pretty much right away.

>
> /dev/rmt/0 <-- The Tape Drive with no options.
> /dev/rmt/0cbn <-- What you should be using. Enables HW compression and tells 
> the tape drive to not automatically rewind.
>
> The key being the 'c' in the device name. If you don't have that, then under 
> Solaris the drive will not compress using its internal hardware compression.
>
> Keep in mind though, if you are sending non-compressible binary files, 400GB 
> is what you are going to get, regardless of if the client or drive is doing 
> the compression. If you're sending highly compressible files (images for 
> example) then you will get very good compression and your tape capacity will 
> lean closer to the 800GB mark. If you're sending a mixture, then you will get 
> somewhere between the two (depending on the type of files).
Yep, in some cases I've sent highly compressed files and I have seen the ratio 
as low as 0.92:1.

Justin.

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