Red Hat Bugzilla – Bug 814824
Support thin pools with non-power-of-2 block sizes between 64K and 1G, in 64K increments
Last modified: 2013-02-21 03:09:37 EST
Make dm thin bug 814823 available through lvm2.
This request was not resolved in time for the current release. Red Hat invites you to ask your support representative to propose this request, if still desired, for consideration in the next release of Red Hat Enterprise Linux.
This request was erroneously removed from consideration in Red Hat Enterprise Linux 6.4, which is currently under development. This request will be evaluated for inclusion in Red Hat Enterprise Linux 6.4.
QE reviewed this BZ for QA_ACK but was unable to ack due to a lack of requirements or description of how the new feature is supposed to work or be tested. Please see https://wiki.test.redhat.com/ClusterStorage/WhyNoAck
QA planning phase ends Aug 10th (tomorrow), without more information this feature will likely be nacked by QA. https://engineering.redhat.com/program/rhel/rhel-6-4-0/
This bugzilla should be tested by specifying --chunksize from range 64K to 1G - which could be divided by 4K (so 64K, 68K....) Unlike currently where use could select 64K, 128K, 256K.... Advantage here should be, that if striped LV is used for thin pool the better matching chunksize could be use for non power of 2 stripe sizes.
Adding QA ack for 6.4. Devel will need to provide unit testing results however before this bug can be ultimately verified by QA.
Upstream support with: https://www.redhat.com/archives/lvm-devel/2012-October/msg00071.html Example of usage: lvcreate -T vg/thin -c 192 -L20M Limitation: User may use chunk_size as multiple of 64KiB (the minimal chunk size) While using non-power-of-2 chunk size discards has to use 'ignore' mode (lvcreate will issue a warning for such case and use this mode automatically)
Based on Comment #7 marking this as verified, tested only with 64k increments starting at 64k up until 1g. The command executed was properly warning about the change of mode in case of non-power-of-2 chunk sizes, as expected. Tested with: lvm2-2.02.98-3.el6 lvm2-cluster-2.02.98-3.el6 device-mapper-1.02.77-3.el6 kernel-2.6.32-343.el6
(In reply to comment #7) > Limitation: > > User may use chunk_size as multiple of 64KiB (the minimal chunk size) > While using non-power-of-2 chunk size discards has to use 'ignore' mode > (lvcreate will issue a warning for such case and use this mode automatically) This limitation doesn't exist in RHEL6.4 kernel (see rhel6.git commit 74e8b7d48b378 "dm-thin: support discard with non power of two blocksize")! Kabi, I really think this needs to be resolved.
It's already in upstream lvm git. It should be part of next lvm RHEL6.4 build. https://www.redhat.com/archives/lvm-devel/2012-November/msg00062.html https://www.redhat.com/archives/lvm-devel/2012-November/msg00060.html
I updated the subject, and will mark this verified based on those requirements (and not what's in comment #5). 2.6.32-343.el6.x86_64 lvm2-2.02.98-4.el6 BUILT: Wed Dec 5 08:35:04 CST 2012 lvm2-libs-2.02.98-4.el6 BUILT: Wed Dec 5 08:35:04 CST 2012 lvm2-cluster-2.02.98-4.el6 BUILT: Wed Dec 5 08:35:04 CST 2012 udev-147-2.43.el6 BUILT: Thu Oct 11 05:59:38 CDT 2012 device-mapper-1.02.77-4.el6 BUILT: Wed Dec 5 08:35:04 CST 2012 device-mapper-libs-1.02.77-4.el6 BUILT: Wed Dec 5 08:35:04 CST 2012 device-mapper-event-1.02.77-4.el6 BUILT: Wed Dec 5 08:35:04 CST 2012 device-mapper-event-libs-1.02.77-4.el6 BUILT: Wed Dec 5 08:35:04 CST 2012 cmirror-2.02.98-4.el6 BUILT: Wed Dec 5 08:35:04 CST 2012 SCENARIO - [valid_non_power_2_chunksizes] Create pool volumes using possible (*non* power of 2) chunksizes from 68K to 1048572K Creating [64] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_64 --chunksize 64 -L 2G snapper_thinp Removing [64] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [128] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_128 --chunksize 128 -L 2G snapper_thinp Removing [128] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [192] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_192 --chunksize 192 -L 2G snapper_thinp WARNING: Using discards ignore for chunk size non power of 2. Removing [192] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [256] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_256 --chunksize 256 -L 2G snapper_thinp Removing [256] chunksize thinpool and corresponding thin virtual volume and thin snapshot [...] Creating [712448] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_712448 --chunksize 712448 -L 2G snapper_thinp WARNING: Using discards ignore for chunk size non power of 2. Removing [712448] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [712512] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_712512 --chunksize 712512 -L 2G snapper_thinp WARNING: Using discards ignore for chunk size non power of 2. Removing [712512] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [712576] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_712576 --chunksize 712576 -L 2G snapper_thinp WARNING: Using discards ignore for chunk size non power of 2. Removing [712576] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [712640] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_712640 --chunksize 712640 -L 2G snapper_thinp WARNING: Using discards ignore for chunk size non power of 2. Removing [712640] chunksize thinpool and corresponding thin virtual volume and thin snapshot Deleting VG snapper_thinp Deleting PVs /dev/etherd/e1.1p1 /dev/etherd/e1.1p2
(In reply to comment #17) > Creating [192] chunksize thinpool volume and corresponding thin virtual > volume and thin snapshot > lvcreate --thinpool POOL_192 --chunksize 192 -L 2G snapper_thinp > WARNING: Using discards ignore for chunk size non power of 2. > Removing [192] chunksize thinpool and corresponding thin virtual volume and > thin snapshot This is the 2nd bug I've seen where lvm2 is emitting: "WARNING: Using discards ignore for chunk size non power of 2." As I said before that needs to be fixed for RHEL6.4 (there is no reason to disable discard with non-power of 2 chunksize). Kabi, did that lvm2 fix get flagged for Peter to backport to RHEL6.4 lvm2?
Just a confirmation here. I thought that the warning should have been fixed in the newest version of lvm, namely lvm2-2.02.98-4.el6, but I have it installed and the warnings are still there. Maybe a newer lvm version is needed? When I run a few tests, I am still getting it, like Corey did: Creating with 192 KB chunksize WARNING: Using discards ignore for chunk size non power of 2. Chunk size reported: 192.00k And removing... Creating with 256 KB chunksize Chunk size reported: 256.00k And removing... Creating with 320 KB chunksize WARNING: Using discards ignore for chunk size non power of 2. Chunk size reported: 320.00k And removing...
While the original bug was fix, the new bug was introduced, which unfortunately masked itself with another bug thus technically the while the thin pool was set to 'ignore' discard, the live kernel target has been set in a way to passdown discards so it has passed some basic testing. These 2 upstream patches should beat this issue: https://www.redhat.com/archives/lvm-devel/2012-December/msg00019.html https://www.redhat.com/archives/lvm-devel/2012-December/msg00020.html So for the non-power-of-2 chunk sizes (i.e. -c 192k) passdown should be still supported with latest 6.4 kernel.
No longer seeing "WARNING" messages when running this test case. That said, there are still messages to the console. Should those still exist? [...] device-mapper: thin: Data device (dm-3) discard unsupported: Disabling discard passdown. device-mapper: thin: Data device (dm-3) discard unsupported: Disabling discard passdown. device-mapper: thin: Data device (dm-3) discard unsupported: Disabling discard passdown. device-mapper: thin: Data device (dm-3) discard unsupported: Disabling discard passdown. device-mapper: thin: Data device (dm-3) discard unsupported: Disabling discard passdown. [...] ============================================================ Iteration 2 of 2 started at Wed Dec 12 17:33:50 CST 2012 ============================================================ SCENARIO - [valid_non_power_2_chunksizes] Create pool volumes using possible (*non* power of 2) chunksizes from 68K to 1048572K Creating [64] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_64 --chunksize 64 -L 2G snapper_thinp Removing [64] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [128] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_128 --chunksize 128 -L 2G snapper_thinp Removing [128] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [192] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_192 --chunksize 192 -L 2G snapper_thinp Removing [192] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [256] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_256 --chunksize 256 -L 2G snapper_thinp Removing [256] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [384] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_384 --chunksize 384 -L 2G snapper_thinp Removing [384] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [448] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_448 --chunksize 448 -L 2G snapper_thinp Removing [448] chunksize thinpool and corresponding thin virtual volume and thin snapshot [...] Creating [712448] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_712448 --chunksize 712448 -L 2G snapper_thinp Removing [712448] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [712512] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_712512 --chunksize 712512 -L 2G snapper_thinp Removing [712512] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [712576] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_712576 --chunksize 712576 -L 2G snapper_thinp Removing [712576] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [712640] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_712640 --chunksize 712640 -L 2G snapper_thinp Removing [712640] chunksize thinpool and corresponding thin virtual volume and thin snapshot Creating [1048576] chunksize thinpool volume and corresponding thin virtual volume and thin snapshot lvcreate --thinpool POOL_1048576 --chunksize 1048576 -L 2G snapper_thinp Removing [1048576] chunksize thinpool and corresponding thin virtual volume and thin snapshot Deleting VG snapper_thinp Deleting PVs /dev/sdb1 /dev/sdd1
(In reply to comment #22) > No longer seeing "WARNING" messages when running this test case. That said, > there are still messages to the console. Should those still exist? > > [...] > device-mapper: thin: Data device (dm-3) discard unsupported: Disabling > discard passdown. > device-mapper: thin: Data device (dm-3) discard unsupported: Disabling > discard passdown. > device-mapper: thin: Data device (dm-3) discard unsupported: Disabling > discard passdown. > device-mapper: thin: Data device (dm-3) discard unsupported: Disabling > discard passdown. > device-mapper: thin: Data device (dm-3) discard unsupported: Disabling > discard passdown. > [...] These message states that your 'data' backend device does not support discard operation, thus the pool will operate in no_passdown mode. The future version of lvm might try to detect stacked devices before finalizing table target line and switch to nopassdown with user-space warning. For now it's just kernel information. LVM2 metadata correctly keeps the information about discard passdown, and if the data device would be swapped with a discard-enabled device - it will properly use passdown mode. (Check with lvs -o+discards) So to properly check there is right passdown mode - you could currently look at 'dmsetup status' for thin pool device and try to use with i.e. SSD. For 6.5 there will be improved lvs to display these all this info without dmsetup. For 6.4 version it's expected behavior.
Improvement of lvs is tracked in Bug 908792.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. http://rhn.redhat.com/errata/RHBA-2013-0501.html