Re: Experience with HP Smart Array P400 and SATA drives?

On Wed, Dec 10, 2008 at 5:29 AM, Mario Weilguni <mweilguni(at)sime(dot)com> wrote:
> Aidan Van Dyk schrieb:
>>
>> * Joshua D. Drake <jd(at)commandprompt(dot)com> [081209 11:01]:
>>
>>>
>>> Yes the SmartArray series is quite common and actually know to perform
>>> reasonably well, in RAID 10. You still appear to be trying RAID 5.
>>>
>>
>> *boggle*
>> Are people *still* using raid5?
>>
>> /me gives up!
>>
>>
>
> Why not? I know it's not performing as good as RAID-10, but it does not
> waste 50% diskspace. RAID-6 is no option, because the performance is even
> worse. And, on another system with RAID-5 + spare and SAS drives, the same
> controller is working very well.

I wouldn't refer to it as "waste". It's a tradeoff. With RAID-10 you
get good performance at a cost of having 1/2 the storage capacity of
your drives combined. RAID-5 says you're more worried about your
budget than performance, and sometimes that's the case. The
production servers where I work run a 25G database on a 12 disk
RAID-10. The fact that we get less than a terabyte from 12 147G scsi
disks is no great loss to us, we're interested in having a disk array
that can handle a few 100 transactions per second even if a disk dies.

Also, RAID-6 is faster, IF one of your disks has died (and you're on a
good RAID controller). RAID-5 degraded performance is abysmal even on
good controllers. RAID-10 with a lost disk is about the same as
RAID-10 with all its disks in terms of performance. If you're running
a production 24/7 database server, you can't afford to lose 80%+ of
your throughput when a single drive fails.

But this has all been covered before (many times) both on this list
and over the internet. RAID-5 is useful for large data stores that
can afford downtime. And there are plenty of apps like that. If your
app isn't like that, i.e. needs to be up and performing well 24/7, or
close to it, then RAID5 is a tragic mistake to make.