Chris Hoogendyk wrote:
> 
> Rory Campbell-Lange wrote:
>> Hi Chris
>>
>> On 13/08/09, Chris Hoogendyk (hoogendyk AT bio.umass DOT edu) wrote:
>>   
>> <snip>
>>> Typically, we set up Amanda with holding disk space.
>>>     
>> <snip>
>>
>> If all the storage is locally attached (actually, AoE drives storage
>> units connected over Ethernet), I am hoping to avoid the disk space if I
>> can write to tape fast enough. I'd like to avoid paying for up to 15TB
>> of fast holding disk space if I can avoid it.
> 
> So, one way would be to logically divide the storage into smaller DLE's. 
> A DLE (Disk List Entry -- http://wiki.zmanda.com/man/disklist.5.html) 
> for Amanda can be a mount point or directory. Obviously, I don't know 
> how your storage is organized; but, if you can define your DLE's as 
> separate directories on the storage device, each one of which is much 
> smaller, then you could use a smaller holding disk and still benefit 
> from Amanda's parallelism. In one of the other departments here, the 
> sysadmin has successfully divided a large array this way and is driving 
> LTO4 near top speed.
> 
>>> Compression can be done either on the client, on the server, or on
>>> the tape drive. Obviously, if you use software compression, you want
>>> to turn off the tape drive compression. I use server side
>>> compression, because I have a dedicated Amanda server that can
>>> handle it. By not using the tape drive compression, Amanda has more
>>> complete information on data size and tape usage for its planning.
>>> If your server is more constrained than your clients, you could use
>>> client compression. This is specified in your dumptypes in your
>>> amanda.conf.
>>>     
>> I don't have any clients, so this is an interesting observation. I'll be
>> trying to do sofware compression then I think. The Unix backup book
>> (google for "amanda software compression") suggests that compression can
>> be used on a "per-image basis"; presumably I can pass the backup data
>> stream through gzip or bzip2 on the way to a tape?
> 
> 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.

Frank


-- 
Frank Smith                                      fsmith AT hoovers DOT com
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