Re: 5.1 RAID5 write performance

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Thu, May 05, 2011 at 02:42:17PM -0600, Michael L. Hitch wrote:
> 
>   Well, depending on how the raidframe code actually works, it could
> certainly slow things down quite a bit.  Assuming you are trying to
> write 64k blocks to the block device and a 2K buffer cache size,
> that means the one write of 64k blocks will be split into 32
> buffers, with the data copied from the user address space to the
> buffers.  Then each of those buffers would be written to the raid
> device.  The raidframe driver might them be reading the full data
> strip into buffers, updating the 2K portion corresponding to the
> request, and then writing the full data strip back to the disk.

Ah, yes, the old 
rmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmwrmw
 cycle.  Gets me every time.

Thor