On 4/16/2010 9:52 AM, Daniel Berteaud wrote:
>
>> Just had a thought ... dangerous I know :)
>>
>> Would it improve backuppc performance to use RAID1 with 3 drives?
>> Obviously writes are not improved, but it would seem the majority of
>> work done on the FS are random reads...
>>
>> ie, new files, and unlinks for old expiring files/backups are the only
>> writes (ok, plus logging). Other than that, there is a lot of reading
>> both for every backup as well as for the nightly prune process.
>>
>> Currently, I'm using linux software RAID1 from md, with 2 x 1TB SATAII
>> HDD's, but thinking that adding a third HDD might improve performance
>> (albeit not increasing capacity).
>
> I'm not sure adding a 3rd drive will really improve the performances. If
> you really want better performances, add 2 drives, and go with a RAID10
> setup. This will *really* improve both read and write (but especially
> reads).

Depending on the OS setting, reads are distributed over the raid1 
mirrors so it should give a slight boost by spreading the head motion 
around.   However, I'd expect the same amount of money spent on adding 
RAM to a server to make a much bigger difference by increasing the file 
system/inode cache and eliminating the need for a lot of those reads in 
the first place.

-- 
   Les Mikesell
     lesmikesell AT gmail DOT com

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