I built a level1 raid using a real local device and a network block device.
I specified --bitmap=internal and --write-mostly, --write-behind for
the network block device.
However, when stracing the nbd-server process for this network block
device, I see *reads* more than periodically. One way to get lots of
reads sent to the nbd0 is to fsck /dev/md10.
Why? I know it's called write *mostly* but still it's doing more reads
that I expected (more than 0).
kernel: 2.6.25.18-0.2-default on x86_64, openSUSE 11.0 fully up-to-date.
Here is my --detail:
/dev/md10:
Version : 00.90.03
Creation Time : Fri Dec 5 07:44:41 2008
Raid Level : raid1
Array Size : 78123968 (74.50 GiB 80.00 GB)
Used Dev Size : 78123968 (74.50 GiB 80.00 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 10
Persistence : Superblock is persistent
Intent Bitmap : Internal
Update Time : Fri Dec 5 10:20:49 2008
State : active
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
UUID : 542a0986:dd465da6:b224af07:ed28e4e5
Events : 0.378
Number Major Minor RaidDevice State
0 8 49 0 active sync /dev/sdd1
1 43 0 1 active sync /dev/nbd0
and the result of mdadm --examine-bitmap /dev/nbd0
Filename : /dev/nbd0
Magic : 6d746962
Version : 4
UUID : 542a0986:dd465da6:b224af07:ed28e4e5
Events : 378
Events Cleared : 378
State : OK
Chunksize : 256 KB
Daemon : 5s flush period
Write Mode : Allow write behind, max 256
Sync Size : 78123968 (74.50 GiB 80.00 GB)
Bitmap : 305172 bits (chunks), 0 dirty (0.0%)
--
Jon
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