Re: [ext2resize] Large filesystem resize

[Andreas D. <ad...@tu...>]

On Nov 01, 2001  21:27 -0500, Benjamin Scott wrote:
>   We are considering using ext2resize to expand a 204 GB filesystem by 396
> GB, resulting in a 600 GB filesystem.
> 
>   (1) Has anyone ever tried ext2resize on filesystems this large before?

Yes, in the ext2resize "NEWS" file (maybe only in CVS, I can't remember
if it went into the 1.1.17 release or not) there is a report from a user
going from 150GB -> 240GB -> 463GB.  All went well.

>   (2) Do the people familiar with ext2resize think it will work?
 
Yes.  Granted that I don't get a lot of feedback on ext2resize,
generally people will complain if there is a bug in a program,
especially if it corrupts their data.  I basically never get such
reports.  The only recent emails have either been about the
large_file issue (see below), or requests for ext2online for ext3.

>   (3) Any guesses on how long it will take?

The above report says it took 40 minutes to do the 240->463GB resize.
I don't have details about the system in question.  That was 7 months
ago, so given Moore's law and the fact that you are resizing a larger
filesystem I would say it will take about the same.

To give yourself a comfort factor of to show ext2resize is doing
something, I'd suggest running with "-v" or "-v -d".  The latter may be
too verbose, but it would be very useful to have in case there are any
problems, so you can send it to me - you can tee it to a file, just in
case, like:

ext2resize -v -d <dev_big> 2>&1 | tee /tmp/ext2resize.log

>   (4) Any tips on what I can do to make it go faster, given the large RAM
>       size of the machine?

Deleting files you don't really need will speed things up, since if a file
is in the way of metadata, it will need to be copied to a new location,
whereas less files means less copying.

You will obviously want to do a full fsck before you do the resize,
to ensure that there are no bad things in the fs which may confuse the
resizer. Also, given the fsck time for large filesystems (about 30 minutes
per 100GB is my understanding) you may want to do this in advance if
you have a short outage window.

Also, in light of this you may want to consider using ext3 at some (near)
later date to avoid extended outages.  Ext2resize will work just fine
with unmounted ext3 filesystems also.  Ext3 is very stable on 2.2 kernels.
I used it for a year while I was still on 2.2, without any problems.

>   (5) Are there any pitfalls I should be aware of?

If you have large files (> 2GB) in the filesystem, then the 1.1.17 code
will not work.  It is not so much an issue of the code being broken as
it is of the code (correctly) refusing to resize a filesystem that has
features it does not understand.  However, since the actual file size
is never changed by ext2resize, and any moved inodes are copied directly
from one location to another it turns out that everything is OK.

You can check this in advance with "dumpe2fs -h <dev>" and look for the
"large_file" feature:

$ dumpe2fs -h /dev/vgtest/lvtest
Filesystem volume name:   test fs
Last mounted on:          <not available>
Filesystem UUID:          10921832-6d83-4d21-bb30-3726730bbd4d
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal filetype sparse_super large_file
                                                            ^^^^^^^^^^		
If this is the case, it is a one-line fix+recompile to avoid this problem.
I have just not gotten around to making a new release yet.

It is also a good idea to do a full fsck afterwards, to ensure everything
went well.  The ext2resize code is designed to abort rather than writing
bad data to the disk, but given that I have never personally tested such
large resizes there may be (unlikely) corner cases that are overlooked.
Even during development (i.e. more likely to cause breakage), basically
any ext2resize failure can be corrected by running e2fsck.

Please let me know how things go, so I can add this report to the NEWS
file for the next release.  Obviously, if you have any problems, also
contact me.

Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/