Are you sure about that:
> ...  not be able to stream data to a disk array
If data from NBU policy goes as one stream and you direct them to particular 
arrays
disks (each policy to different disks) it is sequential (not random !) IO 
pattern. In such case even SATA disks
are able to cope with it and deliver high IOPS.

Regards
Przemyslaw Bak (przemol)
--
http://przemol.blogspot.com/


On Wed, May 05, 2010 at 03:43:20PM -0500, Bryan Bahnmiller wrote:
> Agreed.
> 
>   Also, be aware that you will typically not be able to stream data to a 
> disk array as fast as you can to tape drives. (Assuming LTO3 or 4 type 
> performance.) Unless you have a pretty beefy disk array with your RAID 
> configured for streaming. The nice part is that since it is disk, small 
> backups and slow backups won't have "shoeshine" problems like you would 
> with tape.
> 
>    I like to set a high water mark on the disk to keep it at 85% or lower. 
> Generally, 85% full is the point where disk performance starts getting hit 
> hard. Fragmentation will also start hitting the performance hard at that 
> point too.
> 
>    I've yet to see de-staging perform well no matter what the disk array 
> used for the DSSU.
> 
>         Bryan
> 
> 
> 
> 
> Ed Wilts <ewilts AT ewilts DOT org> 
> Sent by: veritas-bu-bounces AT mailman.eng.auburn DOT edu
> 05/05/2010 03:05 PM
> 
> To
> Victor Engle <victor.engle AT gmail DOT com>
> cc
> veritas-bu AT mailman.eng.auburn DOT edu
> Subject
> Re: [Veritas-bu] Architectural question (staging)
> 
> 
> 
> 
> 
> 
> On Wed, May 5, 2010 at 2:57 PM, Victor Engle <victor.engle AT gmail DOT com> 
> wrote:
> So my question is how best to configure the DSSUs with the goal of
> optimized de-staging. I will have 6TB to configure as desired on the
> backup server. If I understand correctly, the more concurrent streams
> allowed to the DSSUs, the slower the de-staging because of interleaved
> backup streams. 
> 
> The DSSU consists of a set of files with each file being a backup image 
> and you define the maximum size of each file within an image.  There is no 
> "interleaving".  When you destage, one image at a time goes to tape.
> 
> Watch your fragment sizes and watch your disk file system 
> fragmentation...  
> 
>    .../Ed
> 
> 
> Ed Wilts, RHCE, BCFP, BCSD, SCSP, SCSE 
> ewilts AT ewilts DOT org
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