[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 

> 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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