zfs scrub enable by default
Bob Friesenhahn
bfriesen at simple.dallas.tx.us
Wed Aug 5 01:21:35 UTC 2020
On Wed, 5 Aug 2020, Grant Gray via freebsd-fs wrote:
>
> 2. That scrubbing PREVENTS data loss. Scrubbing can only tell you about data loss AFTER it happens. Yes, it could alert you to a problem that prevents further data loss, but it's already too late. Scrubbing is not a substitute for RAID, backups and proactive SMART testing.
Any reasonable zfs pool should have sufficient hardware redundancy to
allow it sufficient time to work without losing data before a human is
able to notice and replace the failing hardware.
You make a good point about scrubbing reporting data loss after it
happens, but usually there will not be actual data loss if the pool is
designed properly with sufficient redundancy. In this case, the scrub
failure may be an indication of decreased redundancy and need for
attention from an attendant human. In some cases there might just be
a minor media failure and a resilver will put a redundant copy of the
data elsewhere.
If the pool has more redundancy, then there is less need to scrub it
often. Scrub simple duplex mirrors more often than raidz3.
There is an old saying "If a tree falls in the forest and no one is
there to hear the noise, does it make a sound?". This is somewhat
applicable to zfs since if the data is so derelict that no one
accesses it at all so that it can be detected to be going 'bad', is it
really that important to protect?
Bob
--
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
Public Key, http://www.simplesystems.org/users/bfriesen/public-key.txt
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