On 12/12/2012 06:44 AM, Evgeny Shishkin wrote:
Are you using a hardware based raid controller with them?
Yes, of course. Hardware raid with cache and bbu is a must. You can't get fast fsync without it.
Most SSDs should offer fairly fast fsync without a hardware RAID controller, as they do write-back caching. The trick is to find ones that do write-back caching safely, so you don't get severe data corruption on power-loss.
A HW RAID controller is an absolute must for rotating magnetic media, though.
Also mdadm is a pain in the ass and is suitable only on amazon and other cloud shit.
I've personally been pretty happy with mdadm. I find the array portability it offers very useful, so I don't need to buy a second RAID controller just in case my main controller dies and I need a compatible one to get the array running again. If you don't need a BBU for safe write-back caching then mdadm has advantages over hardware RAID.
I'll certainly use mdadm over onboard fakeraid solutions or low-end hardware RAID controllers. I suspect a mid- to high end HW RAID unit will generally win.
-- Craig Ringer http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services
