Veritas has this feature called fast mirror resync where they have a DRL on each side of the mirror and, detaching/re-attaching a mirror causes only the changed bits to be re-synced. Is anything similar planned for ZFS?
On Wed, Jan 13, 2010 at 4:35 PM, Max Levine <maxpil at gmail.com> wrote:> Veritas has this feature called fast mirror resync where they have ?a > DRL on each side of the mirror and, detaching/re-attaching a mirror > causes only the changed bits to be re-synced. Is anything similar > planned for ZFS?ZFS has that feature from moment zero. -- Regards, Cyril
On Wed, Jan 13, 2010 at 04:38:42PM +0200, Cyril Plisko wrote:> On Wed, Jan 13, 2010 at 4:35 PM, Max Levine <maxpil at gmail.com> wrote: > > Veritas has this feature called fast mirror resync where they have ?a > > DRL on each side of the mirror and, detaching/re-attaching a mirror > > causes only the changed bits to be re-synced.That''s actually a DCO. The DRL is for crash recovery.> > Is anything similar > > planned for ZFS? > > ZFS has that feature from moment zero.I was under the impression that the ZFS fast replay only held for mirrors where one part is "missing" and not where you actually administratively detach it or where the mirror is used on another host (a la ''zpool split''). -- Darren
On January 14, 2010 8:58:51 PM +0000 A Darren Dunham <ddunham at taos.com> wrote:> I was under the impression that the ZFS fast replay only held for > mirrors where one part is "missing" and not where you actually > administratively detach it or where the mirror is used on another host > (a la ''zpool split'').That''s my experience. I wish zfs had that feature. Pretty sure (IIRC) SVM has it with offline/online. -frank
>>>>> "fc" == Frank Cusack <fcusack at fcusack.com> writes:fc> That''s my experience. I wish zfs had that feature. Pretty fc> sure (IIRC) SVM has it with offline/online. zpool offline / zpool online of a mirror component will indeed fast-resync, and I do it all the time. zpool detach / attach will not. no need to guess, just try it. -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 304 bytes Desc: not available URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20100114/c93685e7/attachment.bin>
On Thu, Jan 14, 2010 at 06:11:10PM -0500, Miles Nordin wrote:> zpool offline / zpool online of a mirror component will indeed > fast-resync, and I do it all the time. zpool detach / attach will > not.Yes, but the offline device is still part of the pool. What are you doing with the device when you take it offline? (What''s the reason you''re offlining it?) -- Darren
Perhaps an ISCSI mirror for a laptop? Online it when you are back "home" to keep your backup current. Charles On Thu, Jan 14, 2010 at 7:04 PM, A Darren Dunham <ddunham at taos.com> wrote:> On Thu, Jan 14, 2010 at 06:11:10PM -0500, Miles Nordin wrote: >> zpool offline / zpool online of a mirror component will indeed >> fast-resync, and I do it all the time. ?zpool detach / attach will >> not. > > Yes, but the offline device is still part of the pool. ?What are you > doing with the device when you take it offline? ?(What''s the reason > you''re offlining it?) > > -- > Darren > _______________________________________________ > zfs-discuss mailing list > zfs-discuss at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss >
On Fri, Jan 15, 2010 at 10:37:15AM -0500, Charles Menser wrote:> Perhaps an ISCSI mirror for a laptop? Online it when you are back > "home" to keep your backup current.I do exactly this, but: - It''s not the only thing I do for backup. - The iscsi initiator is currently being a major PITA for me. http://opensolaris.org/jive/thread.jspa?threadID=121484 This kind of sometimes-attached mirror (whether via iscsi, usb disks, or whatever else) is a useful kind of backup for some circumstances, but it is not much good in others. If your need to recover falls into one of those other circumstances, it can be a bit rough. I like it, because: - It''s easy to set up (just a few commands) and (at least ideally) will work basically by itself after that, no thinking required. Those are important characteristics of a good backup! :) - It''s reasonably quick to resilver, and reasonably unintrusive; it can make things slower, but doesn''t prevent normal use while going. - It can be used for repair, rather than recovery, in the case where the laptop disk develops bad sectors, and maybe therefore avoid more complicaed restores and impact analysis. For recently-written data that hasn''t been mirrored, too bad - but it''s more likely to happen to older sectors. Scrub regularly overnight with the mirror attached. However, it falls short of the ideal in a number of ways: - In practice you often need to take some action (plug in usb disk, online/offline the component, clear a fault) to kick it off, and/or to prevent hangs and timeouts when moving away. Sometimes you get those anyway (e.g timing out iscsi during zfs import at boot). - ZFS lacks the ability to assign preference or weights to mirrors for read, so running with the mirror attached can often slow the system down, even when not resilvering. - You mirror everything, including all that scratch data that''s really not worth backing up, the data you already have replicated elsewhere, and those delete actions you did by mistake. - Restores are tricker and can take multiple steps and thinking, especially if you just want some critical data now. It''s hard to know what''s in each backup instance. - The size of the backup is tied to the size of the disk - it''s more complicated to keep more/older backups than are what is on the primary disk, and tricker to restore to a different-sized disk. I keep snapshots of the backing volume so I can have older images (as well as within the backed-up pool), and if I ever need to look inside an image I clone it before importing on the server. Remember to use import -R! I also zfs send -R my pool to another zfs elsewhere, as a second backup. I have some very Q&D hokey scripts for this (which I want to rewrite and make smarter, now that we have snapshot holds), as do other peeople, but there''s not yet quite such an easy setup path for this. I do both things, in the hope that each makes up for the deficiencies of the other. -- Dan. -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 194 bytes Desc: not available URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20100116/299a7e01/attachment.bin>