1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
|
Q: When I access /dev/md0, the kernel spits out a lot of errors like
'md0: device not running, giving up !' and 'I/O error...'. I've
sucessfuly added my devices to the virtual device.
A: To be usable, the device must be running. Use mdrun -px /dev/md0 where
x is l for linear, 0 for raid-0 or 1 for raid-1, or even better, create a
mdtab and do a mdadd -ar.
--
Q: I've created a linear md-dev with 2 devices. /proc/mdstat shows the
total size of the device, but df only shows the size of the first
physical device.
A: You must mkfs your new md-dev before using it the first time, so the
fs will cover the whole device.
--
Q: I've created a raid0 device on /dev/sda2 and /dev/sda3. The device is
a lot slower than a single partition. Is md a real sh*t ?
A: To have a raid0 device running a full speed, you must have partitions
from different disks. You can also tune the chunk size to find the best
performances.
--
Q: mdstop /dev/md0 says that the device is busy.
A: There's a process that keeps a file descriptor on /dev/md0, or
/dev/md0 is still mounted. Terminate the process or umount /dev/md0.
--
Q: How does the chunk size influence the speed of my raid device ?
A: The chunk size is the amount of data contiguous on the virtual device
that is also contiguous on the physical device. Depending on your
workload, the best is to let the chunk size match the size of your
requests, so two requests have chances to be on different disks, and to
be run the same time. This suppose a lot of testing with different chunk
sizes to match the average request size, and to have the best
performances.
|
