Re: Checking the sanity of SATA disks

[Bill Davidsen <davidsen@tmr.com>]

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 <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979