Re: Storage location of temporary files

On Wed, Nov 5, 2008 at 8:22 PM, Gregory Stark <stark@enterprisedb.com> wrote:
>
> "Scott Marlowe" <scott.marlowe@gmail.com> writes:
>
>> 2008/11/5 Christian Schröder <cs@deriva.de>:
>>> Tomasz Ostrowski wrote:
>>>>
>>>> This is wrong. RAID5 is slower than RAID1.
>>>> You should go for RAID1+0 for fast and reliable storage. Or RAID0 for
>>>> even faster but unreliable.
>>>>
>>>
>>> I did not find a clear statement about this. I agree that RAID10 would be
>>> better than RAID5, but in some situations RAID5 at least seems to be faster
>>> than RAID1.
>>
>> For certain read heavy loads RAID-5 will beat RAID-1 handily.  After
>> all, from a read only perspective, a healthy RAID-5 with n disks is
>> equal to a healthy RAID-0 with n-1 disks.
>
> Uhm, and for a read-heavy load a RAID-1 or RAID 1+0 array with n disks is
> equal to a healthy RAID-0 with n disks.

Don't know what testing you've done, but very very few RAID-1 /
RAID-10 setups can equal a RAID-0 setup of the same number of disks.

> RAID-5 should never beat any combination of RAID-0 and RAID-1 with the same
> number of drives at read performance. It's advantage is that you get more
> capacity.

Of course it won't beat a RAID-0 with the same number, but a good
controller is just one disk behind a RAID-0 and RAID-1 controllers
usually don't aggregate RAID-1 reads, but do allow multiple readers to
hit different disks for better concurrent access.  But that's not what
I was talking about.