On 2011-06-16 17:09, Haestan wrote:
I am evaluating hardware for a new PostgreSQL server. For reasons concerning power consumption and available space it should not have more than 4 disks (in a 1U case), if possible. Now, I am not sure what disks to use and how to layout them to get the best performance.
What is your data:memory-size ratio? Can you afford to have everything in memory and only have the disks to be able to sustain writes?
The cheaper option would be to buy 15k Seagate SAS disks with a 3ware 9750SA (battery backed) controller. Does it matter whether to use a 4-disk RAID10 or 2x 2-disk RAID1 (system+pg_xlog , pg_data) setup? Am I right that both would be faster than just using a single 2-disk RAID1 for everything? A higher end option would be to use 2x 64G Intel X-25E SSD's with a LSI MegaRAID 9261 controller for pg_data and/or pg_xlog and 2x SAS disks for the rest. Unfortunately, these SSD are the only ones offered by our supplier and they don't use a supercapacitor, AFAIK. Therefore I would have to disable the write cache on the SSD's somehow and just use the cache on the controller only. Does anyone know if this will work or even uses such a setup.
Any SSD is orders of magnitude better than any rotating drive in terms of random reads. If you will benefit depends on your data:memory ratio..
Furthermore, the LSI MegaRAID 9261 offers CacheCade which uses SSD disks a as secondary tier of cache for the SAS disks. Would this feature make sense for a PostgreSQL server, performance wise?
I have one CacheCade setup... not a huge benefit but it seems measurable. (but really hard to test). .. compared to a full SSD-setup I wouldn't consider it at all. -- Jesper -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
