On 11/02/11 11:39 AM, Thomas Strunz wrote:
For database I assume random read and writes are by way the most important thing and any recent ssd is orders of magnitude faster in that are compared to HDD even the "slow" Intel drives.
actually, SSD's have issues with committed small block (8K) random writes such as databases do a lot of. the SSD has a rather large block size that has to be written all at once, so what they tend to do is accumulate random writes in a buffer, then write them all at once to a contiguous block (remapping the logical LBA sector address to an actual block/offset address).
as a test at work, I compared a 2 x 100GB SAS enterprise SSD RAID0 with a 20 x 146GB SAS 15k HD RAID10, both raids using a HP p410 hardware raid controller with 1Gb cache, and both using XFS. Both file systems are approximately the same in sustainable random writes from postgres, up around 12000 wr/sec during heavy sustained pgbench activity (scaling factor of 500, 48 clients, 24 threads, on a 12 core 24 thread dual xeon e5660 48gb server). The HD raid is faster at sustained large block writes from iozone (1.2GB/sec vs 800MB/sec for the SSD). of course, the HD raid10 is 1.3TB of data, while the SSD raid0 is 200GB of data.
-- john r pierce N 37, W 122 santa cruz ca mid-left coast -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
