Hello,
I have raid 1 which mirrors a root/boot partition on 1SSD and 2HDD (write-mostly). mismatch_cnt goes up even when there are very few writes to the partition as /var is mounted separatly. After I update several packages I typically see mismatch_cnt somewhere between 500,000 and 2,000,000. I have read a number of threads in this DL but could not find an explanation of what could cause mismatch_cnt to grow that much. I checked md5 sums using /var/lib/dpkg/info/*.md5sums, and didn't see many errors, even though there are few, mostly in text files which look ok to me. I guess when I check, all reads go to SSD (as both HDDs in this raid are write-mostly), and thus md5sum only shows no problem on SSD. Note, this partition is used as both boot and root and just in case here is some more info about my system:
root@tbeh:~# uname -a
Linux tbeh 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt11-1 (2015-05-24) x86_64 GNU/Linux
root@tbeh:~# mdadm -D /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Sun Jun 7 18:38:51 2015
Raid Level : raid1
Array Size : 13442048 (12.82 GiB 13.76 GB)
Used Dev Size : 13442048 (12.82 GiB 13.76 GB)
Raid Devices : 3
Total Devices : 3
Persistence : Superblock is persistent
Update Time : Sun Jun 14 08:12:28 2015
State : clean
Active Devices : 3
Working Devices : 3
Failed Devices : 0
Spare Devices : 0
Name : tbeh:0 (local to host tbeh)
UUID : c50d3fbf:5da849fc:9a6872ae:6905e381
Events : 213
Number Major Minor RaidDevice State
0 8 34 0 active sync /dev/sdc2
2 8 18 1 active sync writemostly /dev/sdb2
1 8 2 2 active sync writemostly /dev/sda2
root@tbeh:~# fdisk -l /dev/sdc
Disk /dev/sdc: 111.8 GiB, 120034123776 bytes, 234441648 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x858bea60
Device Boot Start End Sectors Size Id Type
/dev/sdc1 * 2048 50333695 50331648 24G 83 Linux
/dev/sdc2 50333696 77234175 26900480 12.8G da Non-FS data
root@tbeh:~# fdisk -l /dev/sda
Disk /dev/sda: 596.2 GiB, 640135028736 bytes, 1250263728 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x0f06bf61
Device Boot Start End Sectors Size Id Type
/dev/sda1 63 498014 497952 243.1M da Non-FS data
/dev/sda2 498015 27856709 27358695 13G da Non-FS data
/dev/sda3 27856710 35889209 8032500 3.9G da Non-FS data
/dev/sda4 35889210 1250258624 1214369415 579.1G 5 Extended
/dev/sda5 35889273 82782944 46893672 22.4G da Non-FS data
/dev/sda6 82783008 976768064 893985057 426.3G da Non-FS data
/dev/sda7 976768128 1250258624 273490497 130.4G 83 Linux
root@tbeh:~# fdisk -l /dev/sdb
Disk /dev/sdb: 465.8 GiB, 500107862016 bytes, 976773168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x99a9f6d9
Device Boot Start End Sectors Size Id Type
/dev/sdb1 63 498014 497952 243.1M da Non-FS data
/dev/sdb2 498015 27856709 27358695 13G da Non-FS data
/dev/sdb3 27856710 35889209 8032500 3.9G da Non-FS data
/dev/sdb4 35889210 976768064 940878855 448.7G 5 Extended
/dev/sdb5 35889273 82782944 46893672 22.4G da Non-FS data
/dev/sdb6 82783008 976768064 893985057 426.3G da Non-FS data
Just to minize the damage, now I mount / as read only, and remount as rw as necessary. Unfortunatelly right now I don't have anything to update but AFAIR right after package update (and running echo check > /sys/block/md0/md/sync_action) mismatch_cnt wasn't too high, but it went up after I reboot the system (and ran echo check > /sys/block/md0/md/sync_action).
The following may have nothing to do with mismatch_cnt as it's observed even when mismatch_cnt is 0 (after checking of ro partition) but I want to undestand how it's possible.
Cmp of SSD and HDD partitions shows lots of differences
root@tbeh:~# sync; cmp -l /dev/sdc2 /dev/sda2|wc -l
cmp: EOF on /dev/sdc2
1903215
BTW, only first few hundren bytes (at most) have non-zero value on SSD, the rest of differences has 0 bytes on SSD.
4233 0 347
4234 70 65
4235 232 241
4257 0 1
4265 51 264
4266 271 260
4267 14 301
4268 116 317
4269 353 326
4270 21 221
4271 360 176
4272 133 265
4273 154 262
4274 56 120
4275 116 370
4276 304 72
4277 233 62
4278 241 4
4279 161 243
4280 363 353
4281 0 1
4313 31 125
4314 201 173
4315 34 102
4316 15 127
4609 0 376
4610 0 377
4611 0 376
4612 0 377
4613 0 376
4614 0 377
4615 0 376
4616 0 377
4617 0 376
4618 0 377
4619 0 376
4620 0 377
4621 0 376
4622 0 377
4623 0 376
4624 0 377
4625 0 376
4626 0 377
4627 0 376
4628 0 377
4629 0 376
...
I don't see any differences between 2 HDD partitions though.
Does anyone have any idea what could be wrong with my system or what could I try to localize the problem?
Thanks,
Boris
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