On 11/13/09 7:29 AM, "Merlin Moncure" <mmoncure@xxxxxxxxx> wrote: > On Fri, Nov 13, 2009 at 9:48 AM, Scott Marlowe <scott.marlowe@xxxxxxxxx> > wrote: >> I think RAID6 is gonna reduce the throughput due to overhead to >> something far less than what a software RAID-10 would achieve. > > I was wondering about this. I think raid 5/6 might be a better fit > for SSD than traditional drives arrays. Here's my thinking: > > *) flash SSD reads are cheaper than writes. With 6 or more drives, > less total data has to be written in Raid 5 than Raid 10. The main > component of raid 5 performance penalty is that for each written > block, it has to be read first than written...incurring rotational > latency, etc. SSD does not have this problem. > For random writes, RAID 5 writes as much as RAID 10 (parity + data), and more if the raid block size is larger than 8k. With RAID 6 it writes 50% more than RAID 10. For streaming writes RAID 5 / 6 has an advantage however. For SLC drives, there is really not much of a write performance penalty. > -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
