forced fsck (again?)

[Greg Trounson]

Valerie Henson wrote:
...
> This will be ironic coming from me, but I think the ext3 defaults for
> forcing a file system check are a little too conservative for many
> modern use cases.  The two cases I have in mind in particular are:
> 
> * Servers with long uptimes that need very low data unavailability
> times.  Imagine you have a machine room full of servers that have all
> been up and running happily for more than 180 days - the preferred
> case.  Now imagine that the room overheats and the emergency power cut
> is tripped.  Standard heat reduction is swiftly applied (i.e., open
> the door and turn on a fan and hope security doesn't notice) and the
> power turned back on.  Now your entire machine room will be fscking
> for the next 3 hours and whatever service they provide will be
> completely unavailable.  Of course, any admin worth their salt will
> turn off force fsck so it only runs during controlled downtime...
> won't they?

Agreed.  This is a real problem.  And controlled downtime is rather difficult if it takes 
several hours to complete.  You're either without whatever services they provide or with 
reduced redundancy for that time.

> * Laptops.  If suspend and resume doesn't work on your laptop, you'll
> be rebooting (and remounting) a lot, perhaps several times a day.  The
> preferred solution is to get Matthew Garrett to fix your laptop, but
> if you can't, fscking every 10-30 days seems a little excessive.
> Desktop users who shutdown daily to save power will have similar
> problems.  Distros often have the "don't fsck on battery" option and
> some don't use the ext3 defaults for mkfs, but that's only a partial
> solution.  In this case, it's definitely a little much to ask a random
> laptop user to tune their file system.

Agreed again.  Having a laptop insist on an fsck when about to give a presentation to a 
room full of professors is really not a good look.  And being flimsier and more abused 
than desktops, laptops IMO really do need regular checking.

> I'm not sure what the best solution is ...

I am.

Since fscks are unacceptably inconvenient and apparently the only thing worse than 
enforcing periodic fscks is *not* enforcing periodic fscks, then we only have one option. 
  Make fscks less inconvenient.  And since we apparently can't make them any faster, the 
only way I can think of to do that is to add support for (you know what I'm going to say):

Online fscks.

We really, *really* need to support checking of mounted read/write file systems.  I would 
envisage a read-only fsck done on all mounted filesystems regularly, which wouldn't do any 
damage to a file system if implemented properly.  If an inconsistency is picked up, then 
recommend an offline one to be scheduled when the user/admin is ready.

Greg