Re: #blocks per group too big: 37265

[Eric Sandeen <sandeen@redhat.com>]

Paul Slootman wrote:
> Hi,
> I wanted to try out ext4 on my shiny new 9+TB RAID5 device
> (11 x 1TB disks in md raid5).
> 
> I obtained the 1.39-tyt3 version of e2fsprogs, and did:
> 
> ./mkfs.ext3 -j -m 0 -N 1000000000 -O dir_index,filetype,resize_inode -E stride=65536,resize=5120000000 -J device=/dev/mapper/vg11-md15--journal -L data2 /dev/md15
> 
> (If using a separate device for the journal is inadvisable, please let
> me know; this is on a different set of spindles that md15 is running on.)
> 
> The stride was calculated from the 64k chunk of the raid5 device.
> Mainly a guess, as I couldn't find any clear reference on how to plug in
> the values to fill this in.
> 
> Anyway, that did:
> 
> | mke2fs 1.38 (30-Jun-2005)
> | Filesystem label=data2
> | OS type: Linux
> | Block size=4096 (log=2)
> | Fragment size=4096 (log=2)
> | 1000204128 inodes, 2441859680 blocks
> | 0 blocks (0.00%) reserved for the super user
> | First data block=0
> | Maximum filesystem blocks=5485408000
> | 65527 block groups
> | 37265 blocks per group, 37265 fragments per group

I'd probably not use 1.39-tyt3... that's pretty old.  (see the 2005?) :)

I did some >8T work that didn't officially make it in 'til 1.40... I'm
not sure if it's in 1.39-tyt3 or not, I'd guess not.

Also, stride=65536 isn't going to give you what you want, at a minimum
because it's stored in a __u16, and it'll wrap around to 0.  (newer
e2fsprogs fails this way, though it's not clear that that's the reason,
when it fails).

But, if I try bleeding edge e2fsprogs on a semi-similar fs (smaller
stride value just so it doesn't fail):

[tmp]$ /src2/e2fsprogs-git/e2fsprogs/misc/mke2fs -F -j -m 0 -N
1000000000 -O dir_index,filetype,resize_inode -E
stride=13172,resize=5120000000 -J device=journal  -L data2 testfsfile
mke2fs 1.40.8 (13-Mar-2008)
Filesystem label=data2
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
1001548800 inodes, 2441859680 blocks
0 blocks (0.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=4294967296
74520 block groups
32768 blocks per group, 32768 fragments per group
13440 inodes per group
Superblock backups stored on blocks:
	32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
	4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968,
	102400000, 214990848, 512000000, 550731776, 644972544, 1934917632


I at least get a sane blocks per group.

-Eric