dean gaudet wrote:

On Sun, 17 Jun 2007, Wakko Warner wrote:

quoted

quoted

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

I used evms to setup mine.  I have used mdadm in the past.  I use lvm ontop
of it which evms makes it a little easier to maintain.  I have 3 arrays
total (only the raid5 was configured by evms, the other 2 raid1s were done
by hand)

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

I only have 2 ext3 file systems (One of which is mounted R/O since it's
full), all my others are reiserfs (v3).

What benefit would I gain by using an external journel and how big would it
need to be?

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

I specifically didn't use XFS (or JFS) since neither one at the time could
be shrinked.

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