Re: ext4 features (checksums)

Bill Davidsen
2006-07-05T11:58:56Z

Helge Hafting wrote:
> On Tue, Jul 04, 2006 at 01:19:11PM +0200, Krzysztof Halasa wrote:
>> Neil Brown <neilb@suse.de> writes:
>>
>>> With checksums - the filesystem is in a better position to:
>>> - be selective about what is checksummed - no point checksumming
>>> blocks that aren't part of any file. Some blocks (highlevel
>>> metadata) might always be checksummed, while other blocks
>>> (regular data) might not if a 'fast' option was chosen.
>> The same applies to RAID - for example, why "synchronise" unused area?
>>
> Indeed. RAID usually avoid checksumming unused area, it sums on write
> and you don't write "unused" stuff.
>
> Not syncing unused area is possible, if there was a way for raid resync
> to ask the fs what blocks are not in use. I.e. get the
> free block list in disk block order. Then raid resync could skip those.
>
Current RAID code supports having a bitmap of dirty stripes, and can
just sync those during recovery. I'm sure Neil could explain it better,
but this is available without worrying about fs type. Now. Today.

--
Bill Davidsen <davidsen@tmr.com>
Obscure bug of 2004: BASH BUFFER OVERFLOW - if bash is being run by a
normal user and is setuid root, with the "vi" line edit mode selected,
and the character set is "big5," an off-by-one errors occurs during
wildcard (glob) expansion.