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path: root/drivers/md
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2011-07-27MD bitmap: Revert DM dirty log hooksJonathan Brassow
Revert most of commit e384e58549a2e9a83071ad80280c1a9053cfd84c md/bitmap: prepare for storing write-intent-bitmap via dm-dirty-log. MD should not need to use DM's dirty log - we decided to use md's bitmaps instead. Keeping the DIV_ROUND_UP clean-ups that were part of commit e384e58549a2e9a83071ad80280c1a9053cfd84c, however. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27MD: raid1 s/sysfs_notify_dirent/sysfs_notify_dirent_safeJonathan Brassow
If device-mapper creates a RAID1 array that includes devices to be rebuilt, it will deref a NULL pointer when finished because sysfs is not used by device-mapper instantiated RAID devices. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27md/raid5: Avoid BUG caused by multiple failures.NeilBrown
While preparing to write a stripe we keep the parity block or blocks locked (R5_LOCKED) - towards the end of schedule_reconstruction. If the array is discovered to have failed before this write completes we can leave those blocks LOCKED, and init_stripe will notice that a free stripe still has a locked block and will complain. So clear the R5_LOCKED flag in handle_failed_stripe, and demote the 'BUG' to a 'WARN_ON'. Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27md/raid10: move rdev->corrected_errors countingNamhyung Kim
Read errors are considered to corrected if write-back and re-read cycle is finished without further problems. Thus moving the rdev-> corrected_errors counting after the re-reading looks more reasonable IMHO. Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27md/raid5: move rdev->corrected_errors countingNamhyung Kim
Read errors are considered to corrected if write-back and re-read cycle is finished without further problems. Thus moving the rdev-> corrected_errors counting after the re-reading looks more reasonable IMHO. Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27md/raid1: move rdev->corrected_errors countingNamhyung Kim
Read errors are considered to corrected if write-back and re-read cycle is finished without further problems. Thus moving the rdev-> corrected_errors counting after the re-reading looks more reasonable IMHO. Also included a couple of whitespace fixes on sync_page_io(). Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27md: get rid of unnecessary casts on page_address()Namhyung Kim
page_address() returns void pointer, so the casts can be removed. Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27md/raid10: Improve decision on whether to fail a device with a read error.NeilBrown
Normally we would fail a device with a READ error. However if doing so causes the array to fail, it is better to leave the device in place and just return the read error to the caller. The current test for decide if the array will fail is overly simplistic. We have a function 'enough' which can tell if the array is failed or not, so use it to guide the decision. Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27md/raid10: Make use of new recovery_disabled handlingNeilBrown
When we get a read error during recovery, RAID10 previously arranged for the recovering device to appear to fail so that the recovery stops and doesn't restart. This is misleading and wrong. Instead, make use of the new recovery_disabled handling and mark the target device and having recovery disabled. Add appropriate checks in add_disk and remove_disk so that devices are removed and not re-added when recovery is disabled. Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27md: change managed of recovery_disabled.NeilBrown
If we hit a read error while recovering a mirror, we want to abort the recovery without necessarily failing the disk - as having a disk this a read error is better than not having an array at all. Currently this is managed with a per-array flag "recovery_disabled" and is only implemented for RAID1. For RAID10 we will need finer grained control as we might want to disable recovery for individual devices separately. So push more of the decision making into the personality. 'recovery_disabled' is now a 'cookie' which is copied when the personality want to disable recovery and is changed when a device is added to the array as this is used as a trigger to 'try recovery again'. This will allow RAID10 to get the control that it needs. Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27md: remove ro check in md_check_recovery()Namhyung Kim
Commit c89a8eee6154 ("Allow faulty devices to be removed from a readonly array.") added some work on ro array in the function, but it couldn't be done since we didn't allow the ro array to be handled from the beginning. Fix it. Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27md: introduce link/unlink_rdev() helpersNamhyung Kim
There are places where sysfs links to rdev are handled in a same way. Add the helper functions to consolidate them. Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27md/raid: use printk_ratelimited instead of printk_ratelimitChristian Dietrich
As per printk_ratelimit comment, it should not be used. Signed-off-by: Christian Dietrich <christian.dietrich@informatik.uni-erlangen.de> Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27md: use proper little-endian bitopsAkinobu Mita
Using __test_and_{set,clear}_bit_le() with ignoring its return value can be replaced with __{set,clear}_bit_le(). Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> Cc: NeilBrown <neilb@suse.de> Cc: linux-raid@vger.kernel.org Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-27md/raid5: finalise new merged handle_stripe.NeilBrown
handle_stripe5() and handle_stripe6() are now virtually identical. So discard one and rename the other to 'analyse_stripe()'. It always returns 0, so change it to 'void' and remove the 'done' variable in handle_stripe(). Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-27md/raid5: move some more common code into handle_stripeNeilBrown
The RAID6 version of this code is usable for RAID5 providing: - we test "conf->max_degraded" rather than "2" as appropriate - we make sure s->failed_num[1] is meaningful (and not '-1') when s->failed > 1 The 'return 1' must become 'goto finish' in the new location. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-27md/raid5: move more common code into handle_stripeNeilBrown
Apart from 'prexor' which can only be set for RAID5, and 'qd_idx' which can only be meaningful for RAID6, these two chunks of code are nearly the same. So combine them into one adding a test to call either handle_parity_checks5 or handle_parity_checks6 as appropriate. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-27md/raid5: unite handle_stripe_dirtying5 and handle_stripe_dirtying6NeilBrown
RAID6 is only allowed to choose 'reconstruct-write' while RAID5 is also allow 'read-modify-write' Apart from this difference, handle_stripe_dirtying[56] are nearly identical. So resolve these differences and create just one function. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-27md/raid5: unite fetch_block5 and fetch_block6NeilBrown
Provided that ->failed_num[1] is not a valid device number (which is easily achieved) fetch_block6 provides all the functionality of fetch_block5. So remove the latter and rename the former to simply "fetch_block". Then handle_stripe_fill5 and handle_stripe_fill6 become the same and can similarly be united. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-27md/raid5: rearrange a test in fetch_block6.NeilBrown
Next patch will unite fetch_block5 and fetch_block6. First I want to make the differences a little more clear. For RAID6 if we are writing at all and there is a failed device, then we need to load or compute every block so we can do a reconstruct-write. This case isn't needed for RAID5 - we will do a read-modify-write in that case. So make that test a separate test in fetch_block6 rather than merged with two other tests. Make a similar change in fetch_block5 so the one bit that is not needed for RAID6 is clearly separate. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-27md/raid5: move more code into common handle_stripeNeilBrown
The difference between the RAID5 and RAID6 code here is easily resolved using conf->max_degraded. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-27md/raid5: Move code for finishing a reconstruction into handle_stripe.NeilBrown
Prior to commit ab69ae12ceef7 the code in handle_stripe5 and handle_stripe6 to "Finish reconstruct operations initiated by the expansion process" was identical. That commit added an identical stanza of code to each function, but in different places. That was careless. The raid5 code was correct, so move that out into handle_stripe and remove raid6 version. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-27md/raid5: Remove stripe_head_state arg from handle_stripe_expansion.NeilBrown
This arg is only used to differentiate between RAID5 and RAID6 but that is not needed. For RAID5, raid5_compute_sector will set qd_idx to "~0" so j with certainly not equals qd_idx, so there is no need for a guard on that condition. So remove the guard and remove the arg from the declaration and callers of handle_stripe_expansion. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-26md/raid5: move stripe_head_state and more code into handle_stripe.NeilBrown
By defining the 'stripe_head_state' in 'handle_stripe', we can move some common code out of handle_stripe[56]() and into handle_stripe. The means that all accesses for stripe_head_state in handle_stripe[56] need to be 's->' instead of 's.', but the compiler should inline those functions and just use a direct stack reference, and future patches while hoist most of this code up into handle_stripe() so we will revert to "s.". Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-26md/raid5: add some more fields to stripe_head_stateNeilBrown
Adding these three fields will allow more common code to be moved to handle_stripe() struct field rearrangement by Namhyung Kim. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-26md/raid5: unify stripe_head_state and r6_stateNeilBrown
'struct stripe_head_state' stores state about the 'current' stripe that is passed around while handling the stripe. For RAID6 there is an extension structure: r6_state, which is also passed around. There is no value in keeping these separate, so move the fields from the latter into the former. This means that all code now needs to treat s->failed_num as an small array, but this is a small cost. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-26md/raid5: move common code into handle_stripeNeilBrown
There is common code at the start of handle_stripe5 and handle_stripe6. Move it into handle_stripe. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-26md/raid5: replace sh->lock with an 'active' flag.NeilBrown
sh->lock is now mainly used to ensure that two threads aren't running in the locked part of handle_stripe[56] at the same time. That can more neatly be achieved with an 'active' flag which we set while running handle_stripe. If we find the flag is set, we simply requeue the stripe for later by setting STRIPE_HANDLE. For safety we take ->device_lock while examining the state of the stripe and creating a summary in 'stripe_head_state / r6_state'. This possibly isn't needed but as shared fields like ->toread, ->towrite are checked it is safer for now at least. We leave the label after the old 'unlock' called "unlock" because it will disappear in a few patches, so renaming seems pointless. This leaves the stripe 'locked' for longer as we clear STRIPE_ACTIVE later, but that is not a problem. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-26md/raid5: Protect some more code with ->device_lock.NeilBrown
Other places that change or follow dev->towrite and dev->written take the device_lock as well as the sh->lock. So it should really be held in these places too. Also, doing so will allow sh->lock to be discarded. with merged fixes by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-26md/raid5: Remove use of sh->lock in sync_requestNeilBrown
This is the start of a series of patches to remove sh->lock. sync_request takes sh->lock before setting STRIPE_SYNCING to ensure there is no race with testing it in handle_stripe[56]. Instead, use a new flag STRIPE_SYNC_REQUESTED and test it early in handle_stripe[56] (after getting the same lock) and perform the same set/clear operations if it was set. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Namhyung Kim <namhyung@gmail.com>
2011-07-18md/raid5: get rid of duplicated call to bio_data_dir()Namhyung Kim
In raid5::make_request(), once bio_data_dir(@bi) is detected it never (and couldn't) be changed. Use the result always. Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-18md/raid5: use kmem_cache_zalloc()Namhyung Kim
Replace kmem_cache_alloc + memset(,0,) to kmem_cache_zalloc. I think it's not harmful since @conf->slab_cache already knows actual size of struct stripe_head. Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-18md/raid10: share pages between read and write bio's during recoveryNamhyung Kim
When performing a recovery, only first 2 slots in r10_bio are in use, for read and write respectively. However all of pages in the write bio are never used and just replaced to read bio's when the read completes. Get rid of those unused pages and share read pages properly. Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-18md/raid10: factor out common bio handling codeNamhyung Kim
When normal-write and sync-read/write bio completes, we should find out the disk number the bio belongs to. Factor those common code out to a separate function. Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-07-18md/raid10: get rid of duplicated conditional expressionNamhyung Kim
Variable 'first' is initialized to zero and updated to @rdev->raid_disk only if it is greater than 0. Thus condition '>= first' always implies '>= 0' so the latter is not needed. Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-28md: avoid endless recovery loop when waiting for fail device to complete.NeilBrown
If a device fails in a way that causes pending request to take a while to complete, md will not be able to immediately remove it from the array in remove_and_add_spares. It will then incorrectly look like a spare device and md will try to recover it even though it is failed. This leads to a recovery process starting and instantly aborting over and over again. We should check if the device is faulty before considering it to be a spare. This will avoid trying to start a recovery that cannot proceed. This bug was introduced in 2.6.26 so that patch is suitable for any kernel since then. Cc: stable@kernel.org Reported-by: Jim Paradis <james.paradis@stratus.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-14md/raid5: remove unusual use of bio_iovec_idx()Namhyung Kim
In the bio_for_each_segment loop, bvl always points current bio_vec, so the same as bio_iovec_idx(, i). Let's get rid of it. Cc: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-14md/raid5: fix FUA request handling in ops_run_io()Namhyung Kim
Commit e9c7469bb4f5 ("md: implment REQ_FLUSH/FUA support") introduced R5_WantFUA flag and set rw to WRITE_FUA in that case. However remaining code still checks whether rw is exactly same as WRITE or not, so FUAed-write ends up with being treated as READ. Fix it. This bug has been present since 2.6.37 and the fix is suitable for any -stable kernel since then. It is not clear why this has not caused more problems. Cc: Tejun Heo <tj@kernel.org> Cc: stable@kernel.org Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-14md/raid5: fix raid5_set_bi_hw_segmentsNamhyung Kim
The @bio->bi_phys_segments consists of active stripes count in the lower 16 bits and processed stripes count in the upper 16 bits. So logical-OR operator should be bitwise one. This bug has been present since 2.6.27 and the fix is suitable for any -stable kernel since then. Fortunately the bad code is only used on error paths and is relatively unlikely to be hit. Cc: stable@kernel.org Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-09md/bitmap: remove unused fields from struct bitmapNamhyung Kim
Get rid of ->syncchunk and ->counter_bits since they're never used. Also discard COUNTER_BYTE_RATIO which is unused. Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-09md/bitmap: use proper accessor macroNamhyung Kim
Use COUNTER()/NEEDED() macro instead of open-coding them. Signed-off-by: Namhyung Kim <namhyung@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-09md: check ->hot_remove_disk when removing diskNamhyung Kim
Check pers->hot_remove_disk instead of pers->hot_add_disk in slot_store() during disk removal. The linear personality only has ->hot_add_disk and no ->hot_remove_disk, so that removing disk in the array resulted to following kernel bug: $ sudo mdadm --create /dev/md0 --level=linear --raid-devices=4 /dev/loop[0-3] $ echo none | sudo tee /sys/block/md0/md/dev-loop2/slot BUG: unable to handle kernel NULL pointer dereference at (null) IP: [< (null)>] (null) PGD c9f5d067 PUD 8575a067 PMD 0 Oops: 0010 [#1] SMP CPU 2 Modules linked in: linear loop bridge stp llc kvm_intel kvm asus_atk0110 sr_mod cdrom sg Pid: 10450, comm: tee Not tainted 3.0.0-rc1-leonard+ #173 System manufacturer System Product Name/P5G41TD-M PRO RIP: 0010:[<0000000000000000>] [< (null)>] (null) RSP: 0018:ffff880085757df0 EFLAGS: 00010282 RAX: ffffffffa00168e0 RBX: ffff8800d1431800 RCX: 000000000000006e RDX: 0000000000000001 RSI: 0000000000000002 RDI: ffff88008543c000 RBP: ffff880085757e48 R08: 0000000000000002 R09: 000000000000000a R10: 0000000000000000 R11: ffff88008543c2e0 R12: 00000000ffffffff R13: ffff8800b4641000 R14: 0000000000000005 R15: 0000000000000000 FS: 00007fe8c9e05700(0000) GS:ffff88011fa00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 0000000000000000 CR3: 00000000b4502000 CR4: 00000000000406e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Process tee (pid: 10450, threadinfo ffff880085756000, task ffff8800c9f08000) Stack: ffffffff8138496a ffff8800b4641000 ffff88008543c268 0000000000000000 ffff8800b4641000 ffff88008543c000 ffff8800d1431868 ffffffff81a78a90 ffff8800b4641000 ffff88008543c000 ffff8800d1431800 ffff880085757e98 Call Trace: [<ffffffff8138496a>] ? slot_store+0xaa/0x265 [<ffffffff81384bae>] rdev_attr_store+0x89/0xa8 [<ffffffff8115a96a>] sysfs_write_file+0x108/0x144 [<ffffffff81106b87>] vfs_write+0xb1/0x10d [<ffffffff8106e6c0>] ? trace_hardirqs_on_caller+0x111/0x135 [<ffffffff81106cac>] sys_write+0x4d/0x77 [<ffffffff814fe702>] system_call_fastpath+0x16/0x1b Code: Bad RIP value. RIP [< (null)>] (null) RSP <ffff880085757df0> CR2: 0000000000000000 ---[ end trace ba5fc64319a826fb ]--- Signed-off-by: Namhyung Kim <namhyung@gmail.com> Cc: stable@kernel.org Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-09md: Using poll /proc/mdstat can monitor the events of adding a spare disks马建朋
Signed-off-by: majianpeng <majianpeng@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-09MD: use is_power_of_2 macroJonathan Brassow
Make use of is_power_of_2 macro. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-09MD: raid5 do not set fullsyncJonathan Brassow
Add check to determine if a device needs full resync or if partial resync will do RAID 5 was assuming that if a device was not In_sync, it must undergo a full resync. We add a check to see if 'saved_raid_disk' is the same as 'raid_disk'. If it is, we can safely skip the full resync and rely on the bitmap for partial recovery instead. This is the legitimate purpose of 'saved_raid_disk', from md.h: int saved_raid_disk; /* role that device used to have in the * array and could again if we did a partial * resync from the bitmap */ Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-09MD: support initial bitmap creation in-kernelJonathan Brassow
Add bitmap support to the device-mapper specific metadata area. This patch allows the creation of the bitmap metadata area upon initial array creation via device-mapper. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-08MD: add sync_super to mddev_t structJonathan Brassow
Add the 'sync_super' function pointer to MD array structure (struct mddev_s) If device-mapper (dm-raid.c) is to define its own on-disk superblock and be able to load it, there must still be a way for MD to initiate superblock updates. The simplest way to make this happen is to provide a pointer in the MD array structure that can be set by device-mapper (or other module) with a function to do this. If the function has been set, it will be used; otherwise, the method with be looked up via 'super_types' as usual. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-08MD: raid1 changes to allow use by device mapperJonathan Brassow
MD RAID1: Changes to allow RAID1 to be used by device-mapper (dm-raid.c) Added the necessary congestion function and conditionalize calls requiring an array 'queue' or 'gendisk'. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-08MD: move thread wakeups into resumeJonathan Brassow
Move personality and sync/recovery thread starting outside md_run. Moving the wakeup's of the personality and sync/recovery threads out of md_run and into do_md_run and mddev_resume solves two issues: 1) It allows bitmap_load to be called before the sync_thread is run and 2) when MD personalities are used by device-mapper (dm-raid.c), the start-up of the array is better alligned with device-mapper primatives (CTR/resume/suspend/DTR). I/O - in this case, recovery operations - should not happen until after a resume has taken place. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: NeilBrown <neilb@suse.de>
2011-06-08MD: possible typoJonathan Brassow
Make message a bit clearer by s/blocks/k/ I chose 'k' vs 'kiB' or 'kB' because it is what is used earlier in the message. 'k' may be a bit ambigous, but I think it's better than "blocks" which normally means 512, but means 1024 in MD. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: NeilBrown <neilb@suse.de>