Clinton Lee Taylor wrote:
Greetings ...
2009/9/2 Bill Davidsen <davidsen@xxxxxxx>:
Clinton Lee Taylor wrote:
http://www.issociate.de/board/post/498227/Ext3_convert_to_RAID1_....html
Wanting to convert an already created and populated ext3 filesystem.
I unmounted the filesystem, ran e2fsck -f /dev/sdb1 to check that the
current filesystem had no errors.
Then ran mdadm --create /dev/md0 --level=1 -n 1 /dev/sdb1 --force to
create the RAID1 device, answered yes to the question.
Right here is where you invite problems.
This just a warning or have you had problems doing this?
If you don't remember to shrink the filesystem you lose data. The list
has had tales of woe from people who have done it. I personally
haven't. Oh, and shrinking a filesystem is not totally without
possibility of having problems due to hardware or power issues or even
just a crash.
Doing it the other way avoids this, all failures keep the original data safe.
- create an array using the NEW partition
- make the filesystem on the new array
- mount the new filesystem
- copy the data to the new array and verify
- umount the old partition
- mount the array on the OLD mount point
- add the OLD partition to the array and let the system refresh it
You want to create the array using
the new device or partition, and put a new filesystem on it.
No, I want to convert an existing ext3 to RAID1 partition ...
See above, you want to wind up with the data on an array, preferably
without modifying the old data until the old data has been moved and
verified.
Read and
understand the man page for mke2fs in the stride= and stripe-width=
parameters, it shouldn't matter for raid-1 but would if you use raid-[56].
How would striding effect RAID growing or shrinking? Does not the
striding just effect performance or is it a big problem? Would a RAID
defragger help?
On raid-[456] it can improve performance. I mentioned it because people
overlook it. And if I were doing this I would use raid-10 to get better
performance, but that's me.
Then mount the array, copy the data to the array, verify it, and then
unmount the old partition and add it.
I know this is a tried, tested and accept procedure to
transfer/transform an existing ext3 partition to a RAID partition, but
this takes allot of data coping and requires double extra storage ...
You are going to use the NEW partition as part of the array anyway, it
takes no extra storage.
What I'm trying to get right, is to create and test a procedure ( with
audience help and peer review ), to convert an ext3 partition to a
RAID1, maybe later other RAID, but this is a first step/test ...
Using a missing disk component should work with any raid level but
raid-0. ;-)
Ran e2fsck -v /dev/md0 to check that the RAID1 device had no
filesystem corruption on it, which it did not.
Added a spared RAID device using mdadm --add /dev/md0 /dev/sdc1
Then grew the RAID1 device to two compents with mdadm --grow /dev/md0
--raid-disks=2 --backup-file=/root/raid1.backup.file
I have an entry in my raid notes which says that's the wrong thing to do,
the array should be created with the correct number of members and one left
"missing" to be added later. My note says it should be done that way, but
not why it's better, but it says "per Neil" so I bet there is a reason. It
does seem to work that way, I just did an adventure in file moving to test
it the hard way. I was doing a mix of raid-1, raid-10, and raid-5 arrays
moving from little drives (750GB) to larger ones.
Okay, but now we have a big question, creating RAID MD with less
devices than they should have should only be done with "missing" or
forced with number of devices? Could the really Neil stand up now?
;-)
I'd like to hear at this point, too. I don't want to modify the old
partition until the new one is working, other than being paranoid is
there a downside to that?
Did another filesystem check once the RAID finished rebuilding and all
seemed fine.
Double checked that the data on the RAID was the same as the original
data by diffing the two, again all was fine.
Now is this just lucky or would this be an acceptable way to convert
an existing ext3 filesystem to RAID1?
See above, given the resize you didn't mention it's okay, but forget the
resize and you risk your data.
Okay, so, you saying that I should make sure that I shrink the ext3
before try and convert, which is what was comment on before ... I only
edited out what I thought was not needed for the basic question of
converting, but, when I write up an article covering this, I will be
sure to detail that and explain that md metadata version 0.90 puts
it's metadata at the end of the device, which should be free, after
the shrink ...
--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
"Now we have another quarterback besides Kurt Warner telling us during postgame
interviews that he owes every great thing that happens to him on a football
field to his faith in Jesus. I knew there had to be a reason why the Almighty
included a mute button on my remote."
-- Arthur Troyer on Tim Tebow (Sports Illustrated)
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