Re: Best hardware/cost tradoff?

>> -----Mensaje original-----
>> De: pgsql-performance-owner(at)postgresql(dot)org
>> * I think we will go for hardware-based RAID 1 with a good
>> battery-backed-up controller. I have read that software RAID
>> perform surprisingly good, but for a production site where
>> hotplug replacement of dead disks is required, is software
>> RAID still worth it?
>> ...
> I havent had any issues with software raid (mdadm) and hot-swaps. It keeps
> working in degraded mode and as soon as you replace the defective disk it
> can reconstruct the array on the fly. Performance will suffer while at it
> but the service keeps up.
> The battery backup makes a very strong point for a hw controller. Still, I
> have heard good things on combining a HW controller with JBODS leaving the
> RAID affair to mdadm. In your scenario though with "*lots* of random reads",
> if I had to choose between a HW controller & 2 disks or software RAID with 4
> or 6 disks, I would go for the disks. There are motherboards with 6 SATA
> ports. For the money you will save on the controller you can afford 6 disks
> in a RAID 10 setup.

This is good advice. Hot-swapping seems cool, but how often will you actually use it? Maybe once every year? With Software RAID, replacing a disk means shutdown, swap the hardware, and reboot, which is usually less than ten minutes, and you're back in business. If that's the only thing that happens, you'll have 99.97% uptime on your server.

If you're on a limited budget, a software RAID 1+0 will be very cost effective and give good performance for lots of random reads. Hardware RAID with a battery-backed cache helps with writes and hot swapping. If your random-read performance needs outweigh these two factors, consider software RAID.

Craig