XO-1.5 users: need your SD card data

Daniel Drake dsd at laptop.org
Mon Apr 25 16:12:59 EDT 2011

On 19 April 2011 15:42, Daniel Drake <dsd at laptop.org> wrote:
> What I was getting confused with is the requirement for inode tables
> to be zeroed out. (this is probably what takes most of the time during
> mke2fs). I might be wrong on that count as well though - its just
> something I picked up in a discussion which I could have
> misunderstood. Probably easy to test: create a file of all 0xff bytes,
> run mke2fs on it, count the number of 0x00 bytes.

I ran this test.
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.

If we were then to go down the route of detecting all-zero blocks and
erase-to-zero cards, we could avoid approximately another 3% of the
writes for ext4 filesystems.


More information about the Devel mailing list