On Jul 02, 2009  15:23 -0700, Justin Maggard wrote:

quoted text
> I've been toying with ext4 and e2fsprogs pu branch (pulled from git

> yesterday) on very large volumes, and I've run into some issues.  What

> I've found so far with an 19TB MD RAID0 volume, running 2.6.29.4 (I'm

> planning on trying 2.6.30 soon):

>

> -  mkfs.ext4 *appears* to work fine, reporting no errors.  Examining

> the superblock info with dumpe2fs -h looks normal -- although I'm

> unfamiliar with "Lifetime writes" field, and I'm not sure why it's at

> 73GB immediately after doing mkfs, before ever mount it.

>

> -  Immediately running e2fsck on the volume before ever mounting it

> will not complete, and results in the following:

> # e2fsck -n /dev/md2

> e2fsck 1.41.7 (29-June-2009)

> Error reading block 2435874816 (Attempt to read block from filesystem

> resulted in short read).  Ignore error? no

> /dev/md2: Attempt to read block from filesystem resulted in short read

> while reading block 2435874816

> /dev/md2: Attempt to read block from filesystem resulted in short read

> reading journal superblock

> e2fsck: Attempt to read block from filesystem resulted in short read

> while checking ext3 journal for /dev/md2

It looks like there may be some problem with the underlying device?

I posted a program here a few months ago called "ll_ver_dev" which

can quickly (or slowly) verify that writes and reads to different

offsets in a block device return consistent data.  The quick version

will detect such problems as 32-bit overflows, but if you are having

strange problems you might need to run the full version.
You could also try running with a filesystem just under 16TB and

verifying that works.
> -  Mounting with -o noload does appear to work, and reading and

quoted text
> writing seems to work fine.

That's because the journal is not being used, which is what seems to

be having the problem.  I wonder if the journal is beyond 8TB or

beyond 16TB for some reason and this is causing grief?
> -  Setting default mount options with tune2fs works fine, as expected.

quoted text
>

> -  Then, I went on to check out filesystem resizing.  I created an LVM

> 15TB LV, and ran mkfs.ext4 on it.  Looking at the superblock info, it

> did not contain the 64bit flag, which I assume is expected behavior.

> I extended the LV to ~18TB and tried resize2fs, and got this error:

> resize2fs: Can't read an block bitmap while trying to resize /dev/data/data0

This is known not to work, AFAIR.
Cheers, Andreas

--

Andreas Dilger

Sr. Staff Engineer, Lustre Group

Sun Microsystems of Canada, Inc.
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