HDD disapears

[Ngjtt]

Hi everybody,
I have been using freenas for quite some time now, but lately I have a problem.
Every now and then one of my drives temporarily becomes unavailable leaving the pool they are in (RAIDZ 5 drives) in a degraded state. When I check the drives the drive is available again and I can simply use replace from the web interface or sometimes if I reboot it automatically detects the drive and my pool is online again. Does anybody has any idea what causes this?
Is it possible that my mobo is faulty? I recently had a power failure (saving up for a UPS now) causing the NAS have a hard power off.

My motherboard is a asrock b75 pro3-m and it holds 5 WD green 2TB drives

 

[cyberjock]

There's lots of possible causes.. bad hard drive, bad SATA cable, bad PSU, bad motherboard(in particular, bad SATA chipset).

So what you need to do is begin ruling those out.

Post the SMART data for the drive in question... that's the easiest to check.

 

[eraser]

I had a similar problem when I enabled periodic SMART tests against my drives a while ago. The last drive attached to my HBA card would drop off during the tests even though the drive was healthy.