On Thu, 17 Mar 2016, Nick Fisk wrote: > There is got to be something else going on here. All that PR does is to > potentially delay the promotion to hit_set_period*recency instead of > just doing it on the 2nd read regardless, it's got to be uncovering > another bug. > > Do you see the same problem if the cache is in writeback mode before you > start the unpacking. Ie is it the switching mid operation which causes > the problem? If it only happens mid operation, does it still occur if > you pause IO when you make the switch? > > Do you also see this if you perform on a RBD mount, to rule out any > librbd/qemu weirdness? > > Do you know if it’s the actual data that is getting corrupted or if it's > the FS metadata? I'm only wondering as unpacking should really only be > writing to each object a couple of times, whereas FS metadata could > potentially be being updated+read back lots of times for the same group > of objects and ordering is very important. > > Thinking through it logically the only difference is that with recency=1 > the object will be copied up to the cache tier, where recency=6 it will > be proxy read for a long time. If I had to guess I would say the issue > would lie somewhere in the proxy read + writeback<->forward logic. That seems reasonable. Was switching from writeback -> forward always part of the sequence that resulted in corruption? Not that there is a known ordering issue when switching to forward mode. I wouldn't really expect it to bite real users but it's possible.. http://tracker.ceph.com/issues/12814 I've opened a ticket to track this: http://tracker.ceph.com/issues/15171 What would be *really* great is if you could reproduce this with a ceph_test_rados workload (from ceph-tests). I.e., get ceph_test_rados running, and then find the sequence of operations that are sufficient to trigger a failure. sage > > > > > -----Original Message----- > > From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of > > Mike Lovell > > Sent: 16 March 2016 23:23 > > To: ceph-users <ceph-users@xxxxxxxxxxxxxx>; sweil@xxxxxxxxxx > > Cc: Robert LeBlanc <robert.leblanc@xxxxxxxxxxxxx>; William Perkins > > <william.perkins@xxxxxxxxxxxxx> > > Subject: Re: data corruption with hammer > > > > just got done with a test against a build of 0.94.6 minus the two commits that > > were backported in PR 7207. everything worked as it should with the cache- > > mode set to writeback and the min_read_recency_for_promote set to 2. > > assuming it works properly on master, there must be a commit that we're > > missing on the backport to support this properly. > > > > sage, > > i'm adding you to the recipients on this so hopefully you see it. the tl;dr > > version is that the backport of the cache recency fix to hammer doesn't work > > right and potentially corrupts data when > > the min_read_recency_for_promote is set to greater than 1. > > > > mike > > > > On Wed, Mar 16, 2016 at 4:41 PM, Mike Lovell > > <mike.lovell@xxxxxxxxxxxxx> wrote: > > robert and i have done some further investigation the past couple days on > > this. we have a test environment with a hard drive tier and an ssd tier as a > > cache. several vms were created with volumes from the ceph cluster. i did a > > test in each guest where i un-tarred the linux kernel source multiple times > > and then did a md5sum check against all of the files in the resulting source > > tree. i started off with the monitors and osds running 0.94.5 and never saw > > any problems. > > > > a single node was then upgraded to 0.94.6 which has osds in both the ssd and > > hard drive tier. i then proceeded to run the same test and, while the untar > > and md5sum operations were running, i changed the ssd tier cache-mode > > from forward to writeback. almost immediately the vms started reporting io > > errors and odd data corruption. the remainder of the cluster was updated to > > 0.94.6, including the monitors, and the same thing happened. > > > > things were cleaned up and reset and then a test was run > > where min_read_recency_for_promote for the ssd cache pool was set to 1. > > we previously had it set to 6. there was never an error with the recency > > setting set to 1. i then tested with it set to 2 and it immediately caused > > failures. we are currently thinking that it is related to the backport of the fix > > for the recency promotion and are in progress of making a .6 build without > > that backport to see if we can cause corruption. is anyone using a version > > from after the original recency fix (PR 6702) with a cache tier in writeback > > mode? anyone have a similar problem? > > > > mike > > > > On Mon, Mar 14, 2016 at 8:51 PM, Mike Lovell > > <mike.lovell@xxxxxxxxxxxxx> wrote: > > something weird happened on one of the ceph clusters that i administer > > tonight which resulted in virtual machines using rbd volumes seeing > > corruption in multiple forms. > > > > when everything was fine earlier in the day, the cluster was a number of > > storage nodes spread across 3 different roots in the crush map. the first > > bunch of storage nodes have both hard drives and ssds in them with the hard > > drives in one root and the ssds in another. there is a pool for each and the > > pool for the ssds is a cache tier for the hard drives. the last set of storage > > nodes were in a separate root with their own pool that is being used for burn > > in testing. > > > > these nodes had run for a while with test traffic and we decided to move > > them to the main root and pools. the main cluster is running 0.94.5 and the > > new nodes got 0.94.6 due to them getting configured after that was > > released. i removed the test pool and did a ceph osd crush move to move > > the first node into the main cluster, the hard drives into the root for that tier > > of storage and the ssds into the root and pool for the cache tier. each set was > > done about 45 minutes apart and they ran for a couple hours while > > performing backfill without any issue other than high load on the cluster. > > > > we normally run the ssd tier in the forward cache-mode due to the ssds we > > have not being able to keep up with the io of writeback. this results in io on > > the hard drives slowing going up and performance of the cluster starting to > > suffer. about once a week, i change the cache-mode between writeback and > > forward for short periods of time to promote actively used data to the cache > > tier. this moves io load from the hard drive tier to the ssd tier and has been > > done multiple times without issue. i normally don't do this while there are > > backfills or recoveries happening on the cluster but decided to go ahead > > while backfill was happening due to the high load. > > > > i tried this procedure to change the ssd cache-tier between writeback and > > forward cache-mode and things seemed okay from the ceph cluster. about > > 10 minutes after the first attempt a changing the mode, vms using the ceph > > cluster for their storage started seeing corruption in multiple forms. the > > mode was flipped back and forth multiple times in that time frame and its > > unknown if the corruption was noticed with the first change or subsequent > > changes. the vms were having issues of filesystems having errors and getting > > remounted RO and mysql databases seeing corruption (both myisam and > > innodb). some of this was recoverable but on some filesystems there was > > corruption that lead to things like lots of data ending up in the lost+found and > > some of the databases were un-recoverable (backups are helping there). > > > > i'm not sure what would have happened to cause this corruption. the libvirt > > logs for the qemu processes for the vms did not provide any output of > > problems from the ceph client code. it doesn't look like any of the qemu > > processes had crashed. also, it has now been several hours since this > > happened with no additional corruption noticed by the vms. it doesn't > > appear that we had any corruption happen before i attempted the flipping of > > the ssd tier cache-mode. > > > > the only think i can think of that is different between this time doing this > > procedure vs previous attempts was that there was the one storage node > > running 0.94.6 where the remainder were running 0.94.5. is is possible that > > something changed between these two releases that would have caused > > problems with data consistency related to the cache tier? or otherwise? any > > other thoughts or suggestions? > > > > thanks in advance for any help you can provide. > > > > mike > > > > > >
_______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
