I think the exception may be when doing a recursive snapshot - ZFS appears to 
halt IO so that it can take all the snapshots at the same instant.

At least, that's what it looked like to me. I've got an Opensolaris ZFS box 
providing NFS to VMWare, and I was getting SCSI timeout's within the Virtual 
Machines that appeared to happen exactly as the snapshots were taken.

When I turned off the recursive snapshots, and rather had each FS snapshot 
individually, the problem went away.

Regards,
        Tristan.

-----Original Message-----
From: zfs-discuss-boun...@opensolaris.org 
[mailto:zfs-discuss-boun...@opensolaris.org] On Behalf Of Richard Elling
Sent: Saturday, 14 November 2009 5:02 AM
To: Rodrigo E. De León Plicet
Cc: zfs-discuss@opensolaris.org
Subject: Re: [zfs-discuss] Snapshot question


On Nov 13, 2009, at 6:43 AM, Rodrigo E. De León Plicet wrote:

> While reading about NILFS here:
>
> http://www.linux-mag.com/cache/7345/1.html
>
>
> I saw this:
>
> One of the most noticeable features of NILFS is that it can  
> "continuously and automatically save instantaneous states of the  
> file system without interrupting service". NILFS refers to these as  
> checkpoints. In contrast, other file systems such as ZFS, can  
> provide snapshots but they have to suspend operation to perform the  
> snapshot operation. NILFS doesn't have to do this. The snapshots  
> (checkpoints) are part of the file system design itself.
>
> I don't think that's correct. Can someone clarify?

It sounds to me like they confused Solaris UFS with ZFS.  What they
say applies to UFS, but not ZFS.
  -- richard

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