Re: ext4 64bit (disk >16TB) question

Goswin von Brederlow
2008-07-15T21:03:35Z

Ric Wheeler <ricwheeler@gmail.com> writes:

> Andreas Dilger wrote:
>> Jose,
>> while waiting for the "efficient bitmap" support, how hard would it be
>> to implement "inefficient bitmaps" that just malloc some GB of memory
>> if needed? This would at least allow people with huge devices to test
>> mke2fs/ext4/e2fsck in the meantime.
>>
>> Cheers, Andreas
>> --
>> Andreas Dilger
>> Sr. Staff Engineer, Lustre Group
>> Sun Microsystems of Canada, Inc.
>>
>>
>
> I think that would be very useful - how much DRAM would we need for a
> 16TB file system ;-) ?
>
> ric

The patched 1.39 e2fsprogs managed to format a 16TIB under kvm with
1GiB ram and 128k swap. A 32TiB disk format uses nearly 1GiB ram for mkfs
alone and eventualy managed to deadlock the I/O layer in kvm with
1.5GB ram and 128k swap. (Something I'm sure is kvms fault. :)

But fsck is suposed to eat more by a factor (see other mails in
thread). So having 4-16GiB ram is probably recommended for anyone
thinking about testing.

I used the sparse_create script linked on one of the ext4 wiki pages
with a sparse loopback file and used mke2fs -i $((64*1024*1024)) to
speed up things. With that a 16TiB ext4 uses somewhat over 4GiB
freshly formated.

MfG
Goswin