Toby Thain wrote:
Hi,
This is not exactly ZFS specific, but this still seems like a fruitful
place to ask.
It occurred to me today that hot spares could sit in standby (spun down)
until needed (I know ATA can do this, I'm supposing SCSI does too, but I
haven't looked at a spec recently). Does anybody do this? Or does
everybody do this already?
"luxadm stop" will work for many SCSI and FC JBODs. If your drive doesn't
support it, it won't hurt anything, it will just claim "Unsupported" --
not very user friendly, IMHO.
I think it is a good idea, with one potential gotcha. The gotcha is that
it can take 30 seconds or more to spin up. By default, the sd and ssd timeouts
are such that a pending iop will not notice that it took a while to spin up.
However, if you have changed those defaults, as sometimes occurs in high
availability requirements, then you probably shouldn't do this.
Does the tub curve (chance of early life failure) imply that hot spares
should be burned in, instead of sitting there doing nothing from new?
Good question. If you consider that mechanical wear out is what ultimately
causes many failure modes, then the argument can be made that a spun down
disk should last longer. The problem is that there are failure modes which
are triggered by a spin up. I've never seen field data showing the difference
between the two. I spin mine down because they are too loud and consume
more electricity, and electricity is expensive in Southern California.
Just like a data disk, seems to me you'd want to know if a hot spare
fails while waiting to be swapped in. Do they get tested periodically?
Another good question. AFAIK, they are not accessed until needed.
Note: they will be queried on boot which will cause a spin up. I use a cron
job to spin mine down in the late evening.
-- richard
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