So, when you add a log device to a pool, it initiates a resilver. What is it actually doing, though? Isn''t the slog a copy of the in-memory intent log? Wouldn''t it just simply replicate the data that''s in the other log, checked against what''s in RAM? And presumably there isn''t that much data in the slog so there isn''t that much to check? Or is it just doing a generic resilver for the sake of argument because you changed something?
Giovanni Tirloni
2010-Sep-04 06:14 UTC
[zfs-discuss] what is zfs doing during a log resilver?
On Thu, Sep 2, 2010 at 10:18 AM, Jeff Bacon <bacon at walleyesoftware.com>wrote:> So, when you add a log device to a pool, it initiates a resilver. > > What is it actually doing, though? Isn''t the slog a copy of the > in-memory intent log? Wouldn''t it just simply replicate the data that''s > in the other log, checked against what''s in RAM? And presumably there > isn''t that much data in the slog so there isn''t that much to check? > > Or is it just doing a generic resilver for the sake of argument because > you changed something? >Good question. Here it takes little over 1 hour to resilver a 32GB SSD in a mirror. I''ve always wondered what exactly it was doing since it was supposed to be 30 seconds worth of data. It also generates lots of checksum errors. -- Giovanni Tirloni gtirloni at sysdroid.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20100904/4fd7fe03/attachment.html>
Eric D. Mudama
2010-Sep-04 07:23 UTC
[zfs-discuss] what is zfs doing during a log resilver?
On Sat, Sep 4 at 3:14, Giovanni Tirloni wrote:> Good question. Here it takes little over 1 hour to resilver a 32GB SSD in > a mirror. I''ve always wondered what exactly it was doing since it was > supposed to be 30 seconds worth of data. It also generates lots of > checksum errors.An hour? Our boot drives (32GB X25-E) will resilver in about 1 minute. -- Eric D. Mudama edmudama at mail.bounceswoosh.org
On Fri, Sep 3, 2010 at 11:14 PM, Giovanni Tirloni <gtirloni at sysdroid.com> wrote:> Good question. Here it takes little over 1 hour to resilver a 32GB SSD in a > mirror. I''ve always wondered what exactly it was doing since it was supposed > to be 30 seconds worth of data. It also generates lots of checksum errors.I think the amount of time required may be due to the checksum errors that you''re getting. My boot drives (120GB 2.5" drives, 15% used) take about 7 minutes to scrub. Any properly functioning SSD should be much, much faster than that. -B -- Brandon High : bhigh at freaks.com
Giovanni Tirloni wrote:> > > On Thu, Sep 2, 2010 at 10:18 AM, Jeff Bacon <bacon at walleyesoftware.com > <mailto:bacon at walleyesoftware.com>> wrote: > > So, when you add a log device to a pool, it initiates a resilver. > > What is it actually doing, though? Isn''t the slog a copy of the > in-memory intent log? Wouldn''t it just simply replicate the data that''s > in the other log, checked against what''s in RAM? And presumably there > isn''t that much data in the slog so there isn''t that much to check? > > Or is it just doing a generic resilver for the sake of argument because > you changed something? > > > Good question. Here it takes little over 1 hour to resilver a 32GB SSD > in a mirror. I''ve always wondered what exactly it was doing since it was > supposed to be 30 seconds worth of data. It also generates lots of > checksum errors.Here it takes more than 2 days to resilver a failed slog-SSD. I''d also expect it to finish in a few seconds... It seems it resilvers the whole pool, 35T worth of data on 22 spindels (RAID-Z2). We don''t get any errors during resilver. -- Arne
George Wilson
2010-Sep-06 14:42 UTC
[zfs-discuss] what is zfs doing during a log resilver?
Arne Jansen wrote:> Giovanni Tirloni wrote: >> >> >> On Thu, Sep 2, 2010 at 10:18 AM, Jeff Bacon <bacon at walleyesoftware.com >> <mailto:bacon at walleyesoftware.com>> wrote: >> >> So, when you add a log device to a pool, it initiates a resilver. >> >> What is it actually doing, though? Isn''t the slog a copy of the >> in-memory intent log? Wouldn''t it just simply replicate the data >> that''s >> in the other log, checked against what''s in RAM? And presumably there >> isn''t that much data in the slog so there isn''t that much to check? >> >> Or is it just doing a generic resilver for the sake of argument >> because >> you changed something? >> >> >> Good question. Here it takes little over 1 hour to resilver a 32GB SSD >> in a mirror. I''ve always wondered what exactly it was doing since it >> was supposed to be 30 seconds worth of data. It also generates lots of >> checksum errors. > > Here it takes more than 2 days to resilver a failed slog-SSD. I''d also > expect it to finish in a few seconds... It seems it resilvers the whole > pool, > 35T worth of data on 22 spindels (RAID-Z2). > > We don''t get any errors during resilver. > > -- > Arne > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discussResilvering log devices should really be handled differently than other devices in the pool but we don''t do that today. This is documented in CR: 6899591. As a workaround you can first remove the log device and then re-add it to the pool as a mirror-ed log device. - George