Re: partitioned raid 5 and proper partition alignment

Matthias Dahl [off-list ref] writes:

Hi.

On Saturday 08 August 2009 09:56:59 you wrote:

quoted

But each stripe only holds 128k of data. You have to align to that.

I beg to differ. There are two data chunks and one parity chunk, thus a whole 
stripe is 192k long if you've a 64k chunk size. If you align to 128k and you 
put e.g. ext4 on it with the correct fs stride and stripe-width settings, 
you'll probably end up with worse performance since you start in the middle of 
a stripe even though properly aligned to a chunk boundary. Or am I totally on 
the wrong track here...?!

Yes you are. The filesystem will never ever see the parity block of a
stripe. It only ever sees the 128k data. Writing 128k data will write
a full stripe of 192k to disk.

MfG
        Goswin