I have always expected the fall-back behavior of EXT3/2, but recently have not seen it. To be specific, the last time I tried to mount an EXT3 RO, it insisted on trying journal replay. When I marked the disk RO in the block driver, still got attempted replay. (And I/O errors to match the failing write-back of the replay.) When I tried to force mounting as EXT2 (with a "-t ext2"), it still played journal. That was last week. I think the kernel was 2.6.22 which should have a mature EXT3.
So ... I'm not arguing about what EXT3 is supposed to do, but ... my experience does not match my expectation. I therefore recommend EXT2 for any shared RO disk or volume or LUN or partition. (Unless you want to go with ISO-9660, which also works.) -- R; <>< On Wed, Aug 25, 2010 at 08:26, Christian Paro <[email protected]> wrote: > Difference is that ext3 is prepared to fall back to ext2 functionality when > being read from a read-only device - which makes perfect sense, given that > the journal's purpose is to protect the integrity of writes and (as Mark > pointed out) it is of no value on a disk which will never again be written > to. > > ReiserFS, not recognizing that the journal is only relevant when it is > possible to write to the disk, doesn't gracefully fall back to a > journal-less version of itself the way ext3 does. > > As for ext2 vs ext3 for the read-only file system, there is a question of > whether it's a disk which is to be written to once and then linked to and > mounted read-only by everyone (in which case ext2 makes the most sense, with > ext3 adding nothing but unnecessary overhead), or a disk which is regularly > written to by one system - which you for some reason want be able to link to > and mount read-only from another (in which case the ext3 journal does still > serve a purpose while the disk is being accessed in write mode by that first > system). > > On Wed, Aug 25, 2010 at 8:07 AM, Shane <[email protected]> wrote: > >> On Tue, 2010-08-24 at 11:00 -0400, Richard Troth wrote: >> >> > As others have said, ReiserFS wants to replay the journal. EXT3 does >> > too. (Not sure about EXT4.) So for RO I recommend EXT2. >> >> Whilst I'm prepared to believe anything of reiserfs (not having >> attempted to use it since before it was named thus), I query the >> assertion re ext3. Were it to be mounted r/o everywhere, I fail to see >> how the filesystem could have meta-data that would need replaying. >> But I admit to not having specifically tested that - maybe someday. >> >> Shane ... >> >> ---------------------------------------------------------------------- >> For LINUX-390 subscribe / signoff / archive access instructions, >> send email to [email protected] with the message: INFO LINUX-390 or >> visit >> http://www.marist.edu/htbin/wlvindex?LINUX-390 >> ---------------------------------------------------------------------- >> For more information on Linux on System z, visit >> http://wiki.linuxvm.org/ >> > > ---------------------------------------------------------------------- > For LINUX-390 subscribe / signoff / archive access instructions, > send email to [email protected] with the message: INFO LINUX-390 or visit > http://www.marist.edu/htbin/wlvindex?LINUX-390 > ---------------------------------------------------------------------- > For more information on Linux on System z, visit > http://wiki.linuxvm.org/ > ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
