[K12OSN] Need Help
Les Mikesell
les at futuresource.com
Tue Jul 10 06:49:34 UTC 2007
Terrell Prudé Jr. wrote:
>> Are you sure? I have heard that RAID 5 is no good.
>> http://www.baarf.com/
>
> I just looked at this. Whoever these people are, they look to me to be
> ranting. It seems that, to them, nothing short of a multi-node cluster
> filesystem would be enough for your average small-office file server!
> How easy it is to spend other people's money, eh? :-)
Write access is considerably slower on RAID5 and it tends to lock your
heads together even for reads. I've always liked RAID1 for the simple
reason that if everything is broken except one disk you can still
recover the data it held. Plus if you do it in software you don't have
to worry about having to match the controller to read on a different
machine.
> That said, RAID 5 kicks RAID 1 in the delicate parts when it
> comes to performance. Again, we're back to, say, six or eight spindles
> vs. two spindles; no contest.
That's not necessarily true. If you configured those 8 drives in RAID1
pairs, you'd have 4 independently seeking places that could be writing
at once and all 8 would be independent for reads. The trick is to
arrange your data across the partitions so they are likely to be used
simultaneously. These days you could just combine the RAID1 sets into
one LVM, though.
> I've run many 14-disk SCSI RAID 5 setups,
> and my God, they were quick!! Yes, I'm assuming a real hardware RAID
> card here; I generally don't recommend software RAID, no matter which
> RAID level you use.
Software RAID1 works very nicely and does not add much overhead on SCSI
where there is not much CPU interaction anyway. I probably wouldn't do
RAID5 in software.
--
Les Mikesell
lesmikesell at gmail.com
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