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Date:      Fri, 11 Jul 2014 12:30:36 -0700
From:      Freddie Cash <fjwcash@gmail.com>
To:        javocado <javocado@gmail.com>
Cc:        FreeBSD Filesystems <freebsd-fs@freebsd.org>
Subject:   Re: Using 2 SSD's to create a SLOG
Message-ID:  <CAOjFWZ6x6XMD8u=NUapU2ghYi%2BhXH99FkVYrfVARiofkWpOaGQ@mail.gmail.com>
In-Reply-To: <CAP1HOmQuy7kZGg1kKW2=yct_3K50mnws7vQ369jNN3FpMczMvw@mail.gmail.com>
References:  <CAP1HOmRe5hEts6qA=0ZiNbMt%2B%2BDoyJO1f0fs=Wnx4ceC%2BygWeg@mail.gmail.com> <53BD0AFB.3000909@digsys.bg> <CAP1HOmQuy7kZGg1kKW2=yct_3K50mnws7vQ369jNN3FpMczMvw@mail.gmail.com>

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On Fri, Jul 11, 2014 at 12:18 PM, javocado <javocado@gmail.com> wrote:

> Thank you for your feedback. We understand that the devices are mirrored
> and tolerant.
> To further my understanding, confirm that I should be able to yank one of
> the SLOG SSD drives and zfs won't care, and I can subsequently replace it
> (issuing what command?) and zfs will then re-mirror it? And if both drive=
s
> are removed then only the sync data would be lost? But if the drives are
> restored, or in the case of a power loss when the server comes back up, t=
he
> sync data on the SSD's will be processed once zfs starts?
>

http://man.freebsd.org/zpool

:)

Read the parts about "attach" and "detach".

"attach" will add a drive to an existing single-drive vdev, thus converting
it to a 2-way mirror vdev.

"attach" can also be used to add a drive to an existing mirror vdev, thus
converting it to a 3-way=E2=80=8B mirror vdev.

"detach" removes a drive from an existing mirror vdev.

So, if you have a 2-way mirror vdev, and one drive is dying, you can attach
a new drive to it (converting it to a 3-way mirror), wait for it to
resilver, then detach the dying drive.  That way, you never lose redundancy
in the mirror vdev.  :)

=E2=80=8B--
Freddie Cash
fjwcash@gmail.com



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