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Re: Hardware recommendations for Debian server

On Thu, Jun 29, 2006 at 02:06:03AM +0200, martin f krafft wrote:
> also sprach Craig Sanders <cas@taz.net.au> [2006.06.29.0202 +0200]:
> > double for every GB of storage space but it's worth it. it's also
> > faster for read access (but slightly slower for writes).

"slightly slower". i really should have highlighted that the speed
difference is negligible, probably not even noticable. something to be
aware of just for completeness but not something to care about.

> I don't think this is true. If you have the RAID disks on separate
> channels, they'll be fully parallel on writes.

the disks might be able to write in parallel, but linux/the CPU still
has to instruct them to do so in series. first one, then the other. it
doesn't take long at all to fill a disk buffer for write and send the
write commands to the drive, but it takes twice as long to do that twice
as it does to do it once. we're talking microseconds here, so it's not
actually noticable.

> It's true though that the Linux md driver *can* serialise reads and
> improve speed across RAID 0 or 1.

yep.  except you meant to write parallelise, not serialise.


craig sanders <cas@taz.net.au>           (part time cyborg)

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