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SubjectRe: Patch to make ext2 mounts go faster....
From
   Date: 	Mon, 20 Mar 2000 16:57:25 +0100 (MEZ)
From: "Dr. Michael Weller" <eowmob@exp-math.uni-essen.de>

> No, it's best to have extensive checks in user space rather than simple,
> yet expensive, checks in the kernel. The checks have been there forever
> and haven't caught much that isn't caught by the dirty fs flag.

Sorry to jump into this threat. But I have to disagree wholeheartedly!!!!

I experienced myself certain cases of buggy scsi drivers, broken hardware
(scsi, motherboard or memory) wrong setup (dual boot machines with MS Win
and linux and wrong partition setup) where exactly this silly consistency
check came up and pointed out that something odd happened with the disk.
The dirty flag would not deal with that issue.

However, for the majority of desktop linux installations with not that
experienced users (I don't dare to call them admins, although they are the
admins), these tests are sensible and helpful (and the bootup delay caused
is not that high too) and need to be default because they'd not able them
otherwise (because they would not know they should and how).

There are only two problems with your thesis:

(1) The check, although it is quite time consuming, only checks the
bitmaps blocks to see if they match with the superblock group
descriptors. On filesystems with 4k blocks, this means that you only
catch errors that occur in 0.009% of the filesystem. (On filesystems
with 1k blocks, you're cecking 0.03% of the filesystem --- in both
cases, it's well less than a tenth of a percent.) Granted, the bitmap
blocks get written a lot, but it still means that a large number of
potential disk corruptions might not get noticed by the check.

(2) If there are problems, the kernel simply prints a warning.
Many of the non-experienced users are likely to not notice or ignore the
warning messages which appear at boot-time anyway.

(3) If someone *really* wants to do a potentially time-consuming
minimalistic check, I can add it to e2fsck (it's basically means
skipping passes 1 through 4 and only doing pass #5), but quite frankly,
I'm still not convinced its worth the cost/benefit ratio. Still, people
who are really paranoid could use this if they really want.

- Ted


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