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Re: [zfs-discuss] Performance drop during scrub?

Subject: Re: [zfs-discuss] Performance drop during scrub?
From: Bob Friesenhahn
Date: Sun, 2 May 2010 15:12:00 -0500 CDT
On Sun, 2 May 2010, Richard Elling wrote:

These calculations are based on fixed MTBF.  But disk MTBF decreases with
age. Most disks are only rated at 3-5 years of expected lifetime. Hence, 
use solutions with longer lifetimes (high quality tape = 30 years) and plans for
migrating the data to newer media before the expected media lifetime is reached.
In short, if you don't expect to read your 5-year lifetime rated disk for 
another 5 years,
then your solution is uhmm... shall we say... in need of improvement.

Yes, the hardware does not last forever. It only needs to last while it is still being used and should only be used during its expected service life. Your point is a good one.

On the flip-side, using 'zfs scrub' puts more stress on the system which may make it more likely to fail. It increases load on the power supplies, CPUs, interfaces, and disks. A system which might work fine under normal load may be stressed and misbehave under scrub. Using scrub on a weak system could actually increase the chance of data loss.

ZFS storage and performance consulting at http://www.RichardElling.com

Please send $$$ to the above address in return for wisdom.

Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
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