On Fri, 10 Jun 2016, Zdenek Kabelac wrote: > Dne 9.6.2016 v 22:24 Markus Mikkolainen napsal(a): > > I seem to have hit the same snag as Mark describes in his post. > > > > https://www.redhat.com/archives/linux-lvm/2015-April/msg00025.html > > > > with kernel 4.4.6 I detached (--splitcache) a writeback cache from a mounted > > lv which was then synchronized and detached. Then I reattached it and > > shortly > > detached it again. What was interesting is that after the second detach it > > synchronized AGAIN starting from 100% , and then I started getting > > filesystem > > errors. I immediately shutdown, and forced an fsck , and didnt lose that > > much > > data, but still had some stuff to correct. > > > > It looked to me like a detached cache, being reattached will retain all > > cached > > data on it, even though it was supposed to be written to the backing disk, > > and > > then instead of marking it clean on attaching, it will continue serving old > > data from the cache. > > > > > Yes - known issue, --splitcache is rather for 'debugging' purposes. > Use --uncache and create new cache when needed. > > Splitted cache needs to be cleared on reattachment - but that needs further > code rework. It's ok that this is part of a wider picture. If it is imncomplete, it might be wise to block the user from doing the operation, or force them to confirm at the time of reattaching (along with a summary of the risk) Or, if '--splitcache' is completely for debugging purposes, then it probably should be removed from the section "Cache removal" of the lvmcache(7) man page. In my case I was following the instructions on the page, which state that the result is an "unused cache pool LV". I wrongly understood that to mean one which is the same as a newly-created one with the same parameters. As with Markus, I also experienced data corruption which I was lucky to spot, and lucky to have a backup to restore from. > The idea behind is - we want to support 'offline' writeback of data as ATM > cache target doesn't work well if there is any disk error - i.e. cache is in > writeback mode and has 'error' sector - you can't clean such cache... Interesting... is there scope for long-term writeback caching in this design? My own personal use case is I would like to spin down the hard drive in the machine for the majority of the time. Many thanks -- Mark _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
