zfs discuss - Oct 2008 - Change the volblocksize of a ZFS volume

Dear all,

Background:

I have a ZFS volume with the incorrect volume blocksize for the filesystem
(NTFS) that it is supporting.

This volume contains important data that is proving impossible to copy using
Windows XP Xen HVM that "owns" the data.

The disparity in volume blocksize (current set to 512bytes!!) is causing
significant performance problems.

Question :

Is there a way to change the volume blocksize say via ''zfs snapshot
send/receive''?

As I see things, this isn''t possible as the target volume (including
property values) gets overwritten by ''zfs receive''.

Many Thanks for any help.

Nick Smith
--
This message posted from opensolaris.org

Nick Smith wrote:
> Dear all,
>
> Background:
>
> I have a ZFS volume with the incorrect volume blocksize for the filesystem
(NTFS) that it is supporting.
>
> This volume contains important data that is proving impossible to copy
using Windows XP Xen HVM that "owns" the data.
>
> The disparity in volume blocksize (current set to 512bytes!!) is causing
significant performance problems.
>
> Question :
>
> Is there a way to change the volume blocksize say via ''zfs
snapshot send/receive''?
>
> As I see things, this isn''t possible as the target volume
(including property values) gets overwritten by ''zfs receive''.
>   
By default, properties are not received.  To pass properties, you need 
to use
the -R flag.  For examples, see the ZFS Administration Guide,
http://www.opensolaris.org/os/community/zfs/docs/zfsadmin.pdf
 -- richard
> Many Thanks for any help.
>
> Nick Smith
> --
> This message posted from opensolaris.org
> _______________________________________________
> zfs-discuss mailing list
> zfs-discuss at opensolaris.org
> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
>

> > Question :
> >
> > Is there a way to change the volume blocksize say
> via ''zfs snapshot send/receive''?
> >
> > As I see things, this isn''t possible as the target
> volume (including property values) gets overwritten
> by ''zfs receive''.
> >   
> 
> By default, properties are not received.  To pass
> properties, you need 
> to use
> the -R flag.
I have tried that, and while it works for properties like compression, I have
not found a way to preserve a non-default volblocksize across zfs send | zfs
receive. the zvol created on the receive side is always defaulting to 8k. Is
there a way to do this?

Thanks.
-- 
This message posted from opensolaris.org

> > > Question :
> > >
> > > Is there a way to change the volume blocksize
> say
> > via ''zfs snapshot send/receive''?
> > >
> > > As I see things, this isn''t possible as the
> target
> > volume (including property values) gets
> overwritten
> > by ''zfs receive''.
> > >   
> > 
> > By default, properties are not received.  To pass
> > properties, you need 
> > to use
> > the -R flag.
> 
> I have tried that, and while it works for properties
> like compression, I have not found a way to preserve
> a non-default volblocksize across zfs send | zfs
> receive. the zvol created on the receive side is
> always defaulting to 8k. Is there a way to do this?
> 
I spoke too soon. More particularly, during the zfs send/recv processes the
receiving side reports 8k, but once the receive is done the volblocksize is
reporting the expected value as sent with -R.

Hopefully, this is just a reporting bug during an active receive.

Note, this was observed with s10u7 (x86).

Thanks.
-- 
This message posted from opensolaris.org

stuart anderson writes:
 > > > > Question :
 > > > >
 > > > > Is there a way to change the volume blocksize
 > > say
 > > > via ''zfs snapshot send/receive''?
 > > > >
 > > > > As I see things, this isn''t possible as the
 > > target
 > > > volume (including property values) gets
 > > overwritten
 > > > by ''zfs receive''.
 > > > >   
 > > > 
 > > > By default, properties are not received.  To pass
 > > > properties, you need 
 > > > to use
 > > > the -R flag.
 > > 
 > > I have tried that, and while it works for properties
 > > like compression, I have not found a way to preserve
 > > a non-default volblocksize across zfs send | zfs
 > > receive. the zvol created on the receive side is
 > > always defaulting to 8k. Is there a way to do this?
 > > 
 > 
 > I spoke too soon. More particularly, during the zfs send/recv
 > processes the receiving side reports 8k, but once the receive is done
 > the volblocksize is reporting the expected value as sent with -R. 
 > 
 > Hopefully, this is just a reporting bug during an active receive.
 > 
 > Note, this was observed with s10u7 (x86).
 > 

Sounds like so.

I would be very surprised if one would be able to change the
volblocksize of a zvol through send/receive (with or without
-R). It''s an immutable property of the zvol.

-r


 > Thanks.
 > -- 
 > This message posted from opensolaris.org
 > _______________________________________________
 > zfs-discuss mailing list
 > zfs-discuss at opensolaris.org
 > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss