-----Mensaje original-----
De: pgsql-performance-owner@xxxxxxxxxxxxxx
* 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
