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Date:      Sun, 27 Mar 2022 02:02:25 -0400
From:      grarpamp <grarpamp@gmail.com>
To:        freebsd-questions@freebsd.org
Subject:   Re: zfs mirror pool online but drives have read errors
Message-ID:  <CAD2Ti2_igxva3u_U2DtA1-UQyOtLuj4VM3BrQEozNDz37_vJuA@mail.gmail.com>
In-Reply-To: <emf36013e4-0469-47cd-a99d-d06600df1565@winserver>
References:  <emf36013e4-0469-47cd-a99d-d06600df1565@winserver>

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First, make and test some backups with whatever you prefer,
zfs send, rsync, tar...

The zfs got errors, pool had enough read redundancy for
scrubs / silvering to work, drives are failing underneath.

Can also be tried in other box to confirm in isolation...

Test full drive read with...
dd if=/dev/drive of=/dev/null bs=1m conv=noerror

Test full drive write with...
dd if=/dev/random of=/dev/drive bs=1m

With camcontrol you also try standard and manufacturer
drive based sanitize / security erase / initialize functions.

These write operations may map out drive bad sectors
so the next dd read and write tests may be clean.

Then trust the drive again or not.

> It did repair 54M on the last scrub, I did another scrub today and again
> repairs are needed (only 128K this time).

More fails.

> smartctl does see the errors (but still says SMART overall-health
> self-assessment test result: PASSED ):

It's an estimation. Hardware fail is unpredictable.

> -zfs doesn't remove the drives because...

Likely.

> -Both drives are unreliable...

Likely.

> Could more expensive ssd's made a difference here ?

Maybe not, people try to hammer on cheap USB sticks
ZFS arrays thousand of write cycles for fun.

https://www.youtube.com/watch?v=7z526m1jvls

zfs set atime=off compression=on ... saves life too.

> 1200TBW

/2TB = 600 cycles

> "zfs send > imgfile"
> what would have have happened here if more and
> more read errors would occur ?

zpool failmode=wait
If the send completed ok, the image should be good.
Users are supposed to test their backups anyway.



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