On 14/08/09, Frank Smith (fsmith AT hoovers DOT com) wrote:
> Chris Hoogendyk wrote:
> > Amanda will do the compression for you. You define it in the dumptype in 
> > amanda.conf. If you have a holding disk, then it will compress the data 
> > as it goes onto the holding disk. If you don't have a holding disk, then 
> > you might have issues with being able to stream a backup to tape, 
> > compressing it on the fly. Even with a really fast cpu, I don't know if 
> > you can maintain the throughput to drive LTO4 at a good speed.
> 
> You might want to consider configuring for client compression.  Not
> only will that give you more CPU for feeding your tape, it also
> minimizes network bandwidth. As usual, YMMV, it all depends on where
> the bottlenecks are in your environment.

In our case the server _is_ the only client, with up to 30TB of direct
attached storage, with the storage running at between 80MB/s and 120MB/s
access speeds (Bytes rather than bytes).

I don't know if this is fast enough to deal with a SAS connected LTO4
drive, particularly if it is doing software compression along the way.

With reference to Chris Hoogendyk's email "clarification on
parallelism", I am very curious to learn if Amanda "...still require[s]
a DLE to be completed to holding disk before it will send any of it to
tape..." In our case this is a particularly important question as,
although we can add in more AoE storage for a DLE, this will only run at
the speeds above. Do we need a 1TB SAS disk array too?

Rory

-- 
Rory Campbell-Lange
Director
rory AT campbell-lange DOT net

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