On 2012-08-27, at 7:30 AM, raphel johnson wrote:
> I was referring EXT4_IOC_RESIZE_FS ioctl implementation in linux
> kernel ver 3.3.8.
>
> It is given in the code that online shrinking not supported.
>
> if (n_blocks_count < o_blocks_count) {
> /* On-line shrinking not supported */
> ext4_warning(sb, "can't shrink FS - resize aborted");
> return -EINVAL;
> }
>
> I am new to ext4 file system. Could you please tell online shrinking
> issues in ext4.
>
> Thanks in adavance.
There are several reasons for this:
- if blocks are in use beyond the new end of the filesystem, potentially
all inodes in the filesystem need to be scanned to find the owner
- this also causes consistency issues with the page cache, since moving
in-use disk blocks is tricky, and it isn't always possible to remove
them from memory
- if in-use inodes are beyond the end of the new filesystem, potentially
all of the directories in the filesystem need to be scanned to find the
parent directory
- moving inodes in ext4 will also cause the inode number to change, which
would break NFS and potentially other programs
In the end, rarely do users need to shrink a filesystem while mounted, so
the effort and complexity of doing this isn't worthwhile.
Cheers, Andreas
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
