XO-1.5 users: need your SD card data

[John Gilmore]

> On a 1gb partition, mke2fs writes 33555822 bytes of zeroes (32mb).
> Turning this into a zd file results in 251 blocks with the sha256sum
> indicating all-zeroes.
> 
> Your approach of not writing the untouched part of the disk image
> seems like the best opportunity for speeding up fs-update.

There's now a mkfs option that doesn't zero all the inodes while
building the file system.  It instead sets an extent for the inode
tables, in the superblock, and the kernel zeroes more inodes as it
needs to, in parallel with ordinary system operation.  It also has a
similar option for the block groups.  This is the lazy_itable_init
option set with mke2fs -E and the uninit_bg option set with mke2fs -O.

uninit_bg works only with ext4.  I think lazy_itable_init works with
ext3.

	John