Andy Smith wrote:

Hello,

I have a home fileserver with 4 SATA disks in a RAID 5.  As I am
sure you are aware, SATA devices in Linux currently cannot be
queried for SMART info, so I can't do SMART health checks of these
devices.

Also there is still the tendency for Linux Software RAID to kick
devices out of the array as soon as there is any error on them.

I really don't want to be in the situation where a drive dies, I fit
a new one, and during the resync another device is kicked out
because of spontaneously finding a bad sector.

I tried simply doing a

       dd if=/dev/sd[abcd] of=/dev/null

To check each disk in a very unsubtle fashion, but it drives the
load average on the machine way way up (like to 20+) and makes it
very unresponsive (wait several minutes for a keypress to be
acknowledged), even if I run it under nice -n 19.

You (a) want to use larger buffers, and (b) a program which uses 
O_DIRECT for i/o. I had a news server which was running 28 aps until I 
started using dd, then it dropped to 3 aps. Usinf O_DIRECT there is no 
measurable slowdown (and no buffer contention).

-- 
bill davidsen [off-list ref]
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979