[CentOS] reiserfs vs. xfs

Les Mikesell lesmikesell at gmail.com
Thu Sep 8 13:18:18 UTC 2005

On Thu, 2005-09-08 at 07:32, Bryan J. Smith wrote:

> > The reiserfsck runs seemed to work OK so my only complaint
> > about that part is the oddball syntax needed to actually
> > make it fix anything.
> Well, you've had good luck then.

Except that it's a full day of downtime for the service using
the drive...

> > I'm just wondering why it is so likely to need the fsck at
> > all (maybe 50% of my crashes when busy)
> On all filesystems?  Or just 50% chance that one filesystem will need a
> fsck?

All the busy ones. I don't think it is a problem with idle filesystems.

> [ SIDE NOTE from a previous thread:  Another reason to segment your
> filesystems is not only to "localize" any fsck, but segmentation
> actually _reduces_ the risk of needed a fsck because commits are more
> localized/contained (especially to /tmp, /var, etc...). ]

Backuppc conserves space dramatically by hard-linking all duplicates
it finds (with a fairly fast hashing scheme to find them).  Thus
the whole archive has to be on one filesytem.  I currently use
a 250 gig drive and have a little over 100 gigs used (holding what
would be around 900 gigs of raw data before compression and linking). 

> > I thought it was supposed to know what was committed to disk and never
> > leave it in an inconsistent state. 
> Nope.  You through incorrectly.
> The _only_ purpose of journaling is to _reduce_ the time it takes to
> make the filesystem consistent.  That assumes the journaling is good
> and/or the journal replay/unplay works.
> There is absolutely _no_ way to guarantee a commit, although full data
> journaling with a NVRAM board comes close.

I expect to lose data in a crash - I don't expect the system to lose
track of the free/used portion of the disk with a journaling filesystem.
I suppose the best solution is a better UPS, although I also try
to run the backuppc filesystem in software RAID1 between an internal
IDE drive and an external firewire drive and the 2.6 kernel crashes
consistently in a day or less running like that.  It does work well
enough that I can usually add the external drive to the raid, let it
sync up, then fail and remove it.  It is next to impossible
to copy the huge number of hardlinks any other way in a reasonable
of time. 

  Les Mikesell
    lesmikesell at gmail.com

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