Neil Brown <neilb@xxxxxxx> writes:
> On Monday May 25, goswin-v-b@xxxxxx wrote:
>> That really seems to scream for LVM to support more raid levels. It
>> already has linear, raid0 and raid1 support (although I have no idea
>> how device mapper raid1 compares to md raid1).
>
> Note that LVM (a suite of user-space tools) could conceivably use
> md/raid1, md/raid5 etc. The functionality doesn't have to go in dm.
>
> Neil
How would you do this? Worst case you can have a LV made up of totaly
non linear PEs, meaning lots of 4MB (default PE size) big chunks in
random order on random disks.
Do you create a raid1/5 for each stripe? You surely run out of md
devices.
Create dm mappings for all stripe 0s, stripe 1s, stripe 2s, ... and
then a raid1/5 over those stripe devices?
What if the LV has segments with different raid configurations (number
of disks in a stripe or even different levels)? Create a raid for each
segment and then a dm mapping for a linear raid?
You can get a flood of intermediate devices there. A /proc/mdstat with
200 entries would be horrible. iostat output would be totaly
useless. ...
MfG
Goswin
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