fsck, soft-updates, and snapshots

David Cecil david.cecil at nokia.com
Tue Mar 13 04:12:46 UTC 2007


I almost sent this to freebsd-hackers, so please direct me there is that 
list is more appropriate.  I am seeing some problems with soft-updates 
and fsck (I believe) so I have a couple of questions.

Can anyone tell me src/sys/ufs/ffs/README.softupdates and 
README.snapshots are up to date?  The former is dated June 2000, so it's 
almost 7 years old.  The snapshots readme is only 2 years younger and 
mentions the code being alpha-test.

The problems I'm seeing in 6.1 are:
1. After writing a lot if data/files to a filesystem with soft-updates 
enabled, then unmounting or remounting it:
update error: /: blocks <n> files <y>
It appears others have seen this too.  It appears that an attempt to 
flush the buffers to disk as part of the unmount failed.  Is this a 
known issue?

2. I was planning to use soft-updates and then have fsck run in the 
background if necessary on reboot to reclaim any lost blocks (as 
suggested by Kirk's whitepaper(s)).  Normally the filesystem in question 
would be mounted read-only, but will be mounted read-write at times and 
remounted read-only.  Will a background fsck work on a filesystem 
mounted read-only?  Will it operate on a snapshot and if so, can or how 
does it replace the existing filesystem when the snapshot is corrected?

Any advice much appreciated.


Software Engineer
Secure and Mobile Connectivity
Nokia Enterprise Solutions
+61 7 5553 8307 (office)
+61 412 728 222 (cell)

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