[mythtv-users] Disk-drive hiccups

Raymond Wagner raymond at wagnerrp.com
Fri Jun 19 14:15:37 UTC 2009


Bob Sully wrote:
>> I've been using JFS for several years now, and the only time it has ever
>> given me a fault is when I have a machine crash, and then crash again on
>> boot.  It trashes whatever it was writing to the second time, invariably
>> /var/lib/init.d, which then hoses subsequent attempts at booting.  The
>> only way to fix it is to forcefully fsck from single user mode.
>>     
>
> Hmmmm....I've never had that happen; the few times (before this current
> issue) that this box has crashed or had to be rebooted remotely, I've not
> had any problems with JFS filesystems not coming back up cleanly on
> reboot.
>   
 From what I understand, it's a common problem among journaling file 
systems, if perhaps not a common scenario.  If they crash at a time the 
journal is being played back, or otherwise unavailable, the file system 
is now inconsistent, and you have to perform a normal fsck.

The alternative to this is called 'soft updates', where the file system 
driver reorders writes to disk such that in the event of a crash, the 
disk will never be in an inconsistent state.  There is no journal to 
replay, so disks can be mounted and used immediately.  Instead a 
background garbage collection must be run to recover any space that may 
have been allocated but not assigned to a file.  On the down side, this 
can cause problems with RAID cards that do their own write reordering, 
and do not have a battery backup.


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