Re: Do I have a hardware or a software problem?

On Tue, Dec 11, 2012 at 6:03 PM, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
> On 12/12/2012 06:44 AM, Evgeny Shishkin wrote:
>
>
> On Dec 12, 2012, at 2:41 AM, Niels Kristian Schjødt
> <nielskristian(at)autouncle(dot)com> 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.

Also for sequential throughput md RAID is usually faster than most
RAID controllers, even the high end Areca and LSI ones.