forced fsck (again?)
Greg Trounson
gregt at maths.otago.ac.nz
Wed Jan 30 02:01:58 UTC 2008
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
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