Re: [exim] RAID level for mailstore

Marc Perkel wrote:
>
> Tom Brown wrote:
>> Hi
>>
>> I wonder what people think for a RAID level for their mail stores?
>>
>> I can only have RAID 1 or RAID 5 and i dont have many users ~500 so what
>> do people think? This will be on a hardware RAID card but the RAID
>> channel will not be dedicated to the mail store ie there will be another
>> RAID disk sharing the channel.
>>
>> Just want to lay the spindles out 'correctly'
>
> Get a couple seagate baracudda drives that are 750g+ and has the 32mb
> buffer and use raid 1. It's both fast and secure assuming you need speed.
>

RAID 1 is not fast for writes. It OK to store "write once, read many"
data on RAID level 1. Things like applications that once installed are
only launched after that. The problem with RAID 1 is every write has to
hit every disk in the set before it is considered complete. So your
array ends up only being as fast as the slowest drive.

RAID 5 is the way to go for all around performance. It does require a
minimum of 3 disk and you only end up with the storage equal to one less
than the set size (vs. 2 minimum and the storage of 1 in RAID 1). RAID
5 also gets faster and faster the more drives you add to the set (up to
the through-put of the bus). This is because reads and writes are
distributed across each disk. So while one disk would be saturated
under the write load, in a 3 disk, RAID 5 each disk is only seeing 1/3
of the traffic (plus a little over-head for parity data--which improves
with more disks).

For all out performance with total disregard for data safety RAID 0 is
the way to go (it works sort of like RAID 5 with the distribution of
reads/writes, but no overhead computing or recording the parity data).
But if any one disk in a RAID 0 fails all data in the entire array is lost.