I have a raid array, in fact, two raid arrays which are very similar, however one is being written to constantly (by jbd2 it seems) and the other is not. Here are the arrays:
md9 : active raid5 sdl4 sdk4 sdh4 sdb4 11626217472 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/4] [UUUU] bitmap: 2/29 pages [8KB], 65536KB chunk md8 : active raid5 sdf3 sdc3 sda3 sdi3 11626217472 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/4] [UUUU] bitmap: 0/29 pages [0KB], 65536KB chunk
As you can see, no "checking" or anything special is going. Both arrays are 4x 4TB.
So far so good.
Both of these arrays (/dev/md8 and /dev/md9) contain data only, no root filesystem. In fact, they're rarely used by anything at all. Both have a single ext4 partition mounted with
noatime and are "bcache" ready (but there is no cache volume yet):
/dev/bcache0 11T 7.3T 3.6T 67% /mnt/raid5a /dev/bcache1 11T 7.4T 3.5T 68% /mnt/raid5b
/dev/bcache0 /mnt/raid5a ext4 rw,nosuid,nodev,noexec,noatime,data=ordered 0 0 /dev/bcache1 /mnt/raid5b ext4 rw,nosuid,nodev,noexec,noatime,data=ordered 0 0
iostat reports that there is constant writing going to
/dev/bcache1 (and it's backing volume
/dev/md9), while nothing similar is happening to the identical array
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn md8 0.00 0.00 0.00 0 0 bcache0 0.00 0.00 0.00 0 0 md9 1.50 0.00 18.00 0 36 bcache1 1.00 0.00 12.00 0 24 md8 0.00 0.00 0.00 0 0 bcache0 0.00 0.00 0.00 0 0 md9 2.50 0.00 18.00 0 36 bcache1 2.50 0.00 18.00 0 36
This has been going on for hours.
What I tried:
- Killed anything gvfs related.
ps ax |grep gvfsgives zero results now. Writes keep happening.
- Checked with
lsofif anything is happening. It shows nothing.
iotop. I see a process called
[jbd2/bcache1-8]that is often at the top. Nothing similar for the other array.
- I tried unmounting the volume. This works without a hitch and iostat reports no further accesses (seemingly indicating that nobody is using it). Remounting it however triggers these low volume writes again immediately...
I'm very curious what could possibly be writing to this array. As I said, it only contains data, literally one folder and
lost+found, which is empty...