From: Gionatan Danti <g.danti@assyoma.it>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org, g.danti@assyoma.it
Subject: Re: XFS and sector size on thin volumes
Date: Tue, 12 Sep 2017 00:14:19 +0200 [thread overview]
Message-ID: <838841738c3d8ca84328075615f95475@assyoma.it> (raw)
In-Reply-To: <20170909235323.GL17782@dastard>
> If a block device is presented with 512 sectors on 4k-only sector
> drives, then that's a bug. If it's doing so with 512e drives,
> then that's still a bug because it should be presenting as a
> 512 byte logical, 4096 byte physical sector size device and in that
> case mkfs.xfs will choose 4k sectors by default.
>
> IOWs, if the underlying device is correctly presented to mkfs.xfs
> then it will choose the correct sector size by default. dm-thinp
> does the right thing with sector sizes, but I have no idea about
> ZoL.
Hi Dave,
it seems ZVOLs behave... interestingly...
# 4K volume
[root@blackhole ~]# zfs create tank/vol1 -V 300M -b 4k
[root@blackhole ~]# blockdev --getss --getpbsz --getiomin --getioopt
/dev/zvol/tank/vol1
512
4096
4096
4096
# 8K volume
[root@blackhole ~]# zfs create tank/vol1 -V 300M -b 8k
[root@blackhole ~]# blockdev --getss --getpbsz --getiomin --getioopt
/dev/zvol/tank/vol1
512
8192
8192
8192
# 128K volume
[root@blackhole ~]# zfs create tank/vol1 -V 300M -b 128k
[root@blackhole ~]# blockdev --getss --getpbsz --getiomin --getioopt
/dev/zvol/tank/vol1
512
131072
131072
131072
So, it seems that volume's block size does not only change the
iomin/ioopt values, but pbsz also. On the other hand, ss is stuck at
512B, even if I am using a 512e (4K physical sector size) underlying
disk:
[root@blackhole ~]# blockdev --getss --getpbsz --getiomin --getioopt
/dev/sdc
512
4096
4096
0
Creating an XFS filesystem on such a ZVOL will issue the following
message:
"specified blocksize 4096 is less than device physical sector size 8192
switching to logical sector size 512"
In this case, should I specify block size (-b size=4k) at mkfs.xfs time,
or not?
Thanks.
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8
next prev parent reply other threads:[~2017-09-11 22:14 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-09 22:11 XFS and sector size on thin volumes Gionatan Danti
2017-09-09 23:12 ` Dave Chinner
2017-09-09 23:26 ` Gionatan Danti
2017-09-09 23:53 ` Dave Chinner
2017-09-11 22:14 ` Gionatan Danti [this message]
2017-09-11 22:28 ` Eric Sandeen
2017-09-12 5:24 ` Gionatan Danti
2017-09-16 16:43 ` Gionatan Danti
2017-09-16 18:33 ` Eric Sandeen
2017-09-16 19:59 ` Gionatan Danti
2017-09-16 22:01 ` Eric Sandeen
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