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? -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20091113/6a388860/attachment.html>
>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 "continu>ously >> and automatically save instantaneous states of the file system with>out >> interrupting service". NILFS refers to these as checkpoints. In con>trast, >> other file systems such as ZFS, can provide snapshots but they have> to suspend >> operation to perform the snapshot operation. NILFS doesn=E2=80=99t >have to do >> this. The snapshots (checkpoints) are part of the file system desig>n itself. >> * >> > >I don''t think that''s correct. Can someone clarify?No, and they also write this:>More over, creating these checkpoints or snapshots do not result >in decreased performance as they do for file systems such as ZFS.Both are wrong; a snapshot is cheap and doesn''t suspend operations. It''s pretty much like the checkpoints in NILFS. Casper
On Nov 13, 2009, at 6:43 AM, Rodrigo E. De Le?n 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
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-bounces at opensolaris.org [mailto:zfs-discuss-bounces at opensolaris.org] On Behalf Of Richard Elling Sent: Saturday, 14 November 2009 5:02 AM To: Rodrigo E. De Le?n Plicet Cc: zfs-discuss at opensolaris.org Subject: Re: [zfs-discuss] Snapshot question On Nov 13, 2009, at 6:43 AM, Rodrigo E. De Le?n 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 _______________________________________________ zfs-discuss mailing list zfs-discuss at opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
On Nov 13, 2009, at 10:36 PM, Tristan Ball wrote:> 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.Snapshots cause a txg commit, similar to what you get when you run sync. The time required to commit depends on many factors, perhaps the largest of which is the latency of the disk.> > 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.SCSI timeouts?!? How short are their timeouts? By default in Solaris, SCSI timeouts are 60 seconds. Have you seen a recursive snapshot take more than 60 seconds?> > When I turned off the recursive snapshots, and rather had each FS > snapshot individually, the problem went away.There have been performance tweeks over the past few years which can impact snapshot performance, though it is still largely gated by the disk. What release were you running? -- richard> > Regards, > Tristan. > > -----Original Message----- > From: zfs-discuss-bounces at opensolaris.org [mailto:zfs-discuss-bounces at opensolaris.org > ] On Behalf Of Richard Elling > Sent: Saturday, 14 November 2009 5:02 AM > To: Rodrigo E. De Le?n Plicet > Cc: zfs-discuss at opensolaris.org > Subject: Re: [zfs-discuss] Snapshot question > > > On Nov 13, 2009, at 6:43 AM, Rodrigo E. De Le?n 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 > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss > > ______________________________________________________________________ > This email has been scanned by the MessageLabs Email Security System. > For more information please visit http://www.messagelabs.com/email > ______________________________________________________________________