Re: [zfs-discuss] An Academic Sysadmin's Lament for ZFS ?

[Phil Harman]

On 10 Sep 2007, at 16:41, Brian H. Nelson wrote:

Stephen Usher wrote:

Brian H. Nelson:

I'm sure it would be interesting for those on the list if you could

wheel... or at least not fall down the pitfalls.

outline the gotchas so that the rest of us don't have to re-invent the

Also, here's a link to the ufs on zvol blog where I originally found the

idea:

http://blogs.sun.com/scottdickson/entry/fun_with_zvols_-_ufs

Example:


Preparation ...

basket# zfs create -V 10m pool0/v1
basket# newfs /dev/zvol/rdsk/pool0/v1
newfs: /dev/zvol/rdsk/pool0/v1 last mounted as /tmp/v1
newfs: construct a new file system /dev/zvol/rdsk/pool0/v1: (y/n)? y
Warning: 4130 sector(s) in last cylinder unallocated

        10.0MB in 1 cyl groups (14 c/g, 42.00MB/g, 20160 i/g)
super-block backups (for fsck -F ufs -o b=#) at:
32,

basket# mount -r /dev/zvol/dsk/pool0/v1 /tmp/v1


Scenario 1 ...

basket# date >/tmp/v1/f1; zfs snapshot pool0/[EMAIL PROTECTED]
basket# cat /tmp/v1/f1
Mon Sep 10 23:07:42 BST 2007
basket# mount -r /dev/zvol/dsk/pool0/[EMAIL PROTECTED] /tmp/v1s1
basket# ls /tmp/v1s1
f1           lost+found/
basket# cat /tmp/v1s1/f1

basket# date >/tmp/v1/f1; zfs snapshot pool0/[EMAIL PROTECTED]
basket# mount -r /dev/zvol/dsk/pool0/[EMAIL PROTECTED] /tmp/v1s2
basket# cat /tmp/v1s2/f1
Mon Sep 10 23:07:42 BST 2007
basket# cat /tmp/v1/f1
Mon Sep 10 23:09:19 BST 2007




Scenario 2 ...


basket# mount -r /dev/zvol/dsk/pool0/[EMAIL PROTECTED] /tmp/v1s3
mount: Mount point /tmp/v1s3 does not exist.
basket# mkdir /tmp/v1s3
basket# mount -r /dev/zvol/dsk/pool0/[EMAIL PROTECTED] /tmp/v1s3
basket# cat /tmp/v1s3/f2
Mon Sep 10 23:18:17 BST 2007
basket# cat /tmp/v1/f2
Mon Sep 10 23:18:17 BST 2007
basket#

Note: the snapshot is consistent because of the lockfs(1M) calls.


Phil

Not everything I've seen blogged about UFS and zvols fills me with warm fuzzies. For instance, the above takes no account of the fact that the UFS filesystem needs to be in a consistent state before a snapshot is taken - e.g. using lockfs(1M). /dev/zvol/rdsk/pool0/v1: 20446 sectors in 4 cylinders of 48 tracks, 128 sectors Note: the first snapshot sees the file but not the contents, while the second snapshot sees stale data. basket# date >/tmp/v1/f2; lockfs -wf /tmp/v1; zfs snapshot pool0/ [EMAIL PROTECTED]; lockfs -u /tmp/v1

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