cpio to ext4 seems much slower than to ext2, ext3 or xfs

[Eric Sandeen]

Roberto Ragusa wrote:
> Ric Wheeler wrote:
>> In our testing with f12, I build a 60TB ext4 file system with 1 billion
>> small files. A forced fsck of ext4 finished in 2.5 hours give or take a
>> bit :-) The fill was artificial and the file system was not aged, so
>> real world results will probably be slower.
>>
>> fsck time scales mostly with the number of allocated files in my
>> experience. Allocated blocks (fewer very large files) are quite quick.
>>
> 
> What kind of machine did you use?
> 
> With 60TB a simple allocation bitmap for 4k-blocks takes almost 2GB;
> and this is just to detect free space or double allocation of blocks.
> Wow.
> 

The box did have a lot of memory, it's true :)

But ext4 also uses the "uninit_bg" feature:

uninit_bg
  Create  a filesystem without initializing all of the
  block groups.  This feature also  enables  checksums
  and  highest-inode-used  statistics  in  each block-
  group.  This feature can speed  up  filesystem  cre-
  ation   time   noticeably  (if  lazy_itable_init  is
  enabled), and can also reduce e2fsck  time  dramati-
  cally.   It is only supported by the ext4 filesystem
  in recent Linux kernels.

-Eric