Re: RAID 5 write performance

Hi!

Tom Del Rosso wrote:
"Igor Batinic" <_ime_._prezime_@xxxxxxxxxxxxxx> wrote in message
news:g37op6$8pq$1@xxxxxxxxxxxxxxxxxxxxx
>>
Indeed, RAID 5 (usually) is much slower that RAID 1 in such cases,
especially if you use RAID 5 array for such a purpose without a lot of
cache, battery backup etc.

RAID 5 is not recommended array for transaction logs not only in
Exchange environment, but also in all other environments.

But why is it slower in write mode? Does the controller write the parity
multiple times even when all the drives are modified?

Transaction (usually) are small records, and also usually each transaction is written only to one disk in array. RAID 5 is most efficient when "full stroke write" is usual.
That means: if small record is written to only one or two disks in array, worst case scenario is to read data from all other disks, calculate parity and then new data must be written to a couple disks in array.
Therefore RAID 5 is not recommended array for any intensive I/O operation.

Best regards,

Iggy
.

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