On 20.12.2012 09:43, Dave Chinner wrote:
> On Wed, Dec 19, 2012 at 02:04:45AM +0100, Matthias Schniedermeyer wrote:
> > At least i'd count a dropped connection or power failure (The only
> > difference is that in the latter case the cache MAY get dropped,
> > otherwise i'd say both cases are basically the same) among the basic
> > functionality that should be assured by a journaling fileystem.
> A journalling filesystem doesn't guarantee that you won't lose any
> data on crash, power fail or permanent IO errors. All journalling
> guarantees is that the filesystem is *consistent* after recovery.
> i.e. you don't have to run xfs_repair after such a failure to
> ensure it is not corrupted. In all your testing, you have not seen
> the filesystem become corrupted, so the journalling has fulfilled
> it's guarantee.
I know that the basic property of the Journaling is to prevent
corruption of the metadata, IOW to prevent exessive time to check fs
after for e.g. a power-failure.
I'm not arguing that a Journaling FS can't loose any data, only that it
stays "within reason". I think you can agree that hunderds of files
containing hundreds of gigabytes of data is well outside "reasonable
looses". It doesn't have to be a pony or unicorn, but it should at least
be a mule. :-)
Overall i'm quite satisfied with the performance of XFS over the years,
otherwise it wouldn't be the filesystem for over 99.999% of all the
storage capacity i have. The only thing for which i don't use XFS are
"/boot"-partitions, which amount to a few hundreds of MB, whereas XFS
accounts for well over 100TB.
About corruptions: I haven't had any corruption in my dozens of tests,
BUT once my metdadata got corrupted by this bug! (Or mayby the
umount-thing that you meantioned)
It was the first time ever that i had to use xfs_repair (XFS refused to
mount the fs) and i have been using XFS pretty much since it got ported
I "lost" a few files that i had to recover from my last backup (i didn't
bother to look through lost+found). Which luckily i made just minutes
before rebooting the machine in question. I had thought about issuing a
'sync', because the previous incarnation of the bug flashed before my
inner eye. But by the time i had shutdown X and got to the
command-prompt i had already forgotten to type 'sync' and went straight
for 'reboot' and was slightly irritated when my machine did finished
booting correctly, because a secondary-filesystem was MIA. (The
root-filesystem was OK, but my /home was MIA)
The most "pain" i can remeber before this episode was the 0-fill
"thing", which bit me at least once. Other than that it's been smooth
sailing all these years.
I other words: Overall it's still very good work and i will rely on XFS
for the forseable future.