Re: limits on raid

On Sun, 17 Jun 2007, Wakko Warner wrote:

dean gaudet wrote:

quoted

On Sat, 16 Jun 2007, Wakko Warner wrote:

quoted

When I've had an unclean shutdown on one of my systems (10x 50gb raid5) it's
always slowed the system down when booting up.  Quite significantly I must
say.  I wait until I can login and change the rebuild max speed to slow it
down while I'm using it.   But that is another thing.

i use an external write-intent bitmap on a raid1 to avoid this... you 
could use internal bitmap but that slows down i/o too much for my tastes.  
i also use an external xfs journal for the same reason.  2 disk raid1 for 
root/journal/bitmap, N disk raid5 for bulk storage.  no spindles in 
common.

I must remember this if I have to rebuild the array.  Although I'm
considering moving to a hardware raid solution when I upgrade my storage.

you can do it without a rebuild -- that's in fact how i did it the first 
time.

to add an external bitmap:

mdadm --grow --bitmap /bitmapfile /dev/mdX

plus add "bitmap=/bitmapfile" to mdadm.conf... as in:

ARRAY /dev/md4 bitmap=/bitmap.md4 UUID=dbc3be0b:b5853930:a02e038c:13ba8cdc

you can also easily move an ext3 journal to an external journal with 
tune2fs (see man page).

if you use XFS it's a bit more of a challenge to convert from internal to 
external, but see this thread:

http://marc.theaimsgroup.com/?l=linux-xfs&m=106929781232520&w=2

i found that i had to do "sb 1", "sb 2", ..., "sb N" for all sb rather 
than just the "sb 0" that email instructed me to do.

-dean