On Wed, 11 Nov 2009, Nick Guenther wrote:
On Wed, Nov 11, 2009 at 3:35 AM, David Vasek <va...@fido.cz> wrote:
On Tue, 10 Nov 2009, Nick Guenther wrote:
[ext3 data= / FFS]
journal ~= sync (ensures consistency of both metadata and file data)
ordered ~= softdep (ensures consistency of metadata both internally
and with file data)
writeback ~= default (ensures consistency of metadata internally but
real file data may not agree, e.g. my empty file)
Additionally FFS has the async flag which turns off the internal
consistency of the metadata structures; I guess there's no equivalent
for this in ext?
Isn't it rather
default ~= async ?
For ext2, at least.
Well I'm not sure because no one seems to really know. Linux's
mount(1) has this to say:
writeback
Data ordering is not preserved - data may be written
into
the main file system after its metadata has been
commitb
ted to the journal. This is rumoured to be the
highest-
throughput option. It guarantees internal file
system
integrity, however it can allow old data to appear
in
files after a crash and journal recovery.
which seems to imply that metadata is written synchronously (because
it only talks about data appearing in files, not about the whole
filesystem getting trashed).
The paragraph from Linux's mount(1?) you cited is related to ext3/ext4,
which, as tedu@ has already written, uses journaling. Ext2, in contrast,
is mounted async by default.
If still unsure, look at the following document about ext2 from Linux
(kernel) documentation, section Metadata (line 281 and below).
http://www.mjmwired.net/kernel/Documentation/filesystems/ext2.txt
Regards,
David
