Date: Thu, 15 May 2014 13:44:58 +0100 From: "Steven Hartland" <killing@multiplay.co.uk> To: "Michael Jung" <mikej@mikej.com>, <freebsd-fs@freebsd.org> Subject: Re: Understanding ASHIFT SSD and adding a mirrored vdev Message-ID: <426F6341FBF145FA9D98CBA06030CCA6@multiplay.co.uk> References: <5703300e3b052a3f4d14f1957ded08ce@mail.mikej.com>
next in thread | previous in thread | raw e-mail | index | archive | help
----- Original Message -----
From: "Michael Jung" <mikej@mikej.com>
To: <freebsd-fs@freebsd.org>
Sent: Thursday, May 15, 2014 1:14 PM
Subject: Understanding ASHIFT SSD and adding a mirrored vdev
> Hi:
>
> I have read so many threads about ASHIFT on SSD my head is spinning.
> This is my current partition created with a 10-stable installer.
>
> 2x3TB drives in mirror and ashift=12 looks correct. I added the SSD
> which defaulted to ashift=9 and this is where my question is.
>
> Is alignment on SSD important as from what I read we never really know
> the flash layout? I hope there is a simply answer to this ;-)
SSD's are generally 4K devices yes, but they also almost always lie
about their 4k ness, instead reporting 512byte sectors for max
compatibility.
To work around devices which lie FreeBSD has device "quirks", we've
included 4k quirks for quite a large number of SSD's but the list is
ever growning so its not garanteed that your SSD will have a quirk
to correct its lies, if in fact it is lieing.
> Secondly, I want to add another vdev 2x mirrored 3tb drives and it seems
> that ashift would be vdev specific so I would need to gnop the new
> drives before add the new vdev?
I've just MFC'ed r264850 to 10-stable, seems I forgot to tag with MFC so
didn't get a reminder, so if you update to the latest source you'll have
a new sysctl: vfs.zfs.min_auto_ashift
This can be used to force the ashift to be artificually increased, which
is useful for forward compatibility.
> <gnop magic to create partition and set ashift=12>
Instead use: sysctl vfs.zfs.min_auto_ashift=12
> then
>
> zfs add zroot mirror ada3 ada4
Also what is your SSD can you provide the details from:
camcontrol identify ada2
This will allow us to create a new quirk if needed.
Regards
Steve
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?426F6341FBF145FA9D98CBA06030CCA6>