Re: Recommended sw raid setup

Am 02.07.2011 23:30, schrieb Drew:

quoted

I thought that I had read the TLER was not useful for mdraid, so that
enterprise drives were not really advised for mdraid. Am I wrong about
this?

TLER just shortens the firmware's error recovery from something like
60 seconds down to 4 seconds. It's mainly useful in hardware RAID but
I can see it being useful with mdraid in the enterprise where you
can't afford to wait for the drive to do it's own recovery attempts.

This is not correct.  You may want to read the ATA8-ACS2 draft standard
(see www.t13.org).  There you'll find: SCT-ERC

The internal error recovery procedure includes a vast amount of
algorithms.  If a disk cannot read a sector and starts error recovery,
it may take far more than a minute.
With ERC you can tell the disk beforehand to stop processing the command
(may it be "read" or "write") and return a "uncorrectable error" to the
host.  Some drives (i.E. recent Hitachi Deskstar, which I do recommend!)
do not allow you to set ERC lower than 6.5s.

For a home-box I recommend adding a startup-script and a hotplug-script
(as ERC-settings get reset to firmware defaults upon power-on) which
uses smartmontools >=5.41 to set the read-ERC to 7s and the write ERC to
12s.  We have good experience that this works out well in productive
systems.

/Stefan
P.S.: pseudo-knowledge makes important things go really badly wrong.