zfs discuss - Aug 2006 - Unreliable ZFS backups or....

I looked into backing up ZFS and quite honostly I can''t say I am
convinced about its usefullness here when compared to the traditional
ufsdump/restore. While snapshots are nice they can never substitute offline
backups. And although you can keep quite some snapshots lying about it will
consume diskspace, one of the reasons why people also keep offline backups.

However, while you can make one using ''zfs send'' it somewhat
worries me that the only way to perform a restore is by restoring the entire
filesystem (/snapshot). I somewhat shudder at the thought of having to restore
/export/home this way to retrieve but a single file/directory.

Am I overlooking something here or are people indeed resorting to tools like tar
and the likes again to overcome all this? In my opinion ufsdump / ufsrestore was
a major advantage over tar and I really would consider it a major drawback if
that would be the only way to backup data in such a way where it can be more
easily restored.
 
 
This message posted from opensolaris.org

On August 11, 2006 5:25:11 PM -0700 Peter Looyenga <pl at catslair.org>
wrote:
> I looked into backing up ZFS and quite honostly I can''t say I am
convinced about its usefullness
> here when compared to the traditional ufsdump/restore. While snapshots are
nice they can never
> substitute offline backups.
It doesn''t seem to me that they are meant to.
> However, while you can make one using ''zfs send'' it
somewhat worries me that the only way to
> perform a restore is by restoring the entire filesystem (/snapshot). I
somewhat shudder at the
> thought of having to restore /export/home this way to retrieve but a single
file/directory.
You can mitigate this by creating more granular filesystems, e.g. a
filesystem per user homedir.  This has other advantages like per-user
quotas.

-frank

Hello Frank,

Saturday, August 12, 2006, 2:52:40 AM, you wrote:

FC> On August 11, 2006 5:25:11 PM -0700 Peter Looyenga <pl at
catslair.org> wrote:
>
>> However, while you can make one using ''zfs send'' it
somewhat worries me that the only way to
>> perform a restore is by restoring the entire filesystem (/snapshot). I
somewhat shudder at the
>> thought of having to restore /export/home this way to retrieve but a
single file/directory.
FC> You can mitigate this by creating more granular filesystems, e.g. a
FC> filesystem per user homedir.  This has other advantages like per-user
FC> quotas.

I haven''t looked at zfs send/receive code but I guess it should be
possible to add option to restore only selected files instead of full
snapshot.

-- 
Best regards,
 Robert                            mailto:rmilkowski at task.gda.pl
                                       http://milek.blogspot.com

For reasons totally unknown to me (perhaps I missed some explenation somewhere,
its possible) there seems to be forming a discussion through e-mail instead of
these forums. I find this rather peculiar to be honost since I didn''t
use a webforum to be drawn into a mailinglist discussion. Especially if you keep
in mind that when I try to reply to such an email I can only send my response to
the author, mail to the list is rejected. So far for the "whining"
about how I dislike the way this is going.

So, for the people like me who only want to read these forums, responses so far:

[i]You can mitigate this by creating more granular filesystems, e.g. a
filesystem per user homedir.  This has other advantages like per-user
quotas.[/i]

I do hope you''re joking when you think its feasible to backup all those
filesystems on a single basis.
-----
[i]I haven''t looked at zfs send/receive code but I guess it should be
possible to add option to restore only selected files instead of full
snapshot.[/i]

It should indeed but it is not. As the manuals also state:
http://docs.sun.com/app/docs/doc/819-5461/6n7ht6qsc?a=view.

In short: "Saving snapshots ? Use the zfs send and zfs receive commands to
save and restore a ZFS snapshot. You can save incremental changes between
snapshots, but you cannot restore files individually. You must restore the
entire file system snapshot."

And IMO even worse: "When you restore an incremental file system snapshot,
the most recent snapshot must first be rolled back. In addition, the destination
file system must exist.".

I suddenly don''t feel very safe with ZFS anymore to be honost.
-----

What can I say, I think that this is possibly the only drawback to using ZFS,
however I also think it is a major drawback.
 
 
This message posted from opensolaris.org

Yes, before the flames come in I finally realize where I went wrong last night.
Mistook the discussion lists as a mere forum [i]and[/i] also assumed that by
participating with a new discussion I could automaticly participate in full.
I''ll keep that in mind for a possible next time but for now I think
I''d better keep to the common forums.

Sorry for causing any possible inconvenience for people only following this
through e-mail.
 
 
This message posted from opensolaris.org

> Yes, before the flames come in I finally realize where I went wrong last
> night. Mistook the discussion lists as a mere forum [i]and[/i] also assumed
> that by participating with a new discussion I could automaticly participate
> in full. I''ll keep that in mind for a possible next time but for
now I think
> I''d better keep to the common forums.
>
> Sorry for causing any possible inconvenience for people only following this
> through e-mail.
>
I had no problem with your email thread at all.  No worries and I don''t
any cause for concern.

my 0.02 $


-- 
Dennis Clarke

On August 12, 2006 5:06:06 AM -0700 Peter Looyenga <pl at catslair.org>
wrote:
> [i]You can mitigate this by creating more granular filesystems, e.g. a
> filesystem per user homedir.  This has other advantages like per-user
> quotas.[/i]
>
> I do hope you''re joking when you think its feasible to backup all
those
> filesystems on a single basis.
??

I don''t see why this is a problem.

-frank

On Fri, Aug 11, 2006 at 05:25:11PM -0700, Peter Looyenga
wrote:
> I looked into backing up ZFS and quite honostly I can''t say I am
convinced about its usefullness here when compared to the traditional
ufsdump/restore. While snapshots are nice they can never substitute offline
backups. And although you can keep quite some snapshots lying about it will
consume diskspace, one of the reasons why people also keep offline backups.
> 
> However, while you can make one using ''zfs send'' it
somewhat worries me that the only way to perform a restore is by restoring the
entire filesystem (/snapshot). I somewhat shudder at the thought of having to
restore /export/home this way to retrieve but a single file/directory.
To achive that you can combine ZFS snapshots + ZFS send/receive.

[ UFS ]
  - to restore one/two/... files
      use ufsrestore
  - to restore entire filesystem
      use ufsrestore

[ ZFS ]
  - to restore one/two/... files 
      use snapshot(s)
  - to restore entire filesystem 
      use ''zfs receive''

> Am I overlooking something here or are people indeed resorting to tools
like tar and the likes again to overcome all this? In my opinion ufsdump /
ufsrestore was a major advantage over tar and I really would consider it a major
drawback if that would be the only way to backup data in such a way where it can
be more easily restored.
Now in zfs-era :-) it seems we have to change way of thinking about filesystems.
Usually system administrators
are restoring two things:
- particular files
- entire filesystems
Both are achievable by above combination. What is more important is that zfs-way
(restore a file) seems to be easier.
:-)

przemol