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Date:      Wed, 2 Sep 1998 12:16:16 +0200 (CEST)
From:      "D. Rock" <rock@wurzelausix.CS.Uni-SB.DE>
To:        tlambert@primenet.com
Cc:        current@FreeBSD.ORG
Subject:   Re: What the fsck is going on here (disk space vanishing)?
Message-ID:  <199809021016.MAA16571@wurzelausix.cs.uni-sb.de>

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>> Recently, after a kernel panic the system behaves extremely strange:
>> Every time I reboot the machine, I *have* to fsck the / device (I
>> prefer the one / fits all approach), or any write access will result
>> to either "out of inodes" or "no space left on device" errors.
>> Each fsck will change the superblock (FREE BLK COUNT(S) WRONG IN
>> SUPERBLK). df -ki shows up even before the fsck plenty of inodes and
>> blocks left. This error only happens on the 1st drive in the system
>> (Seagate ST32122A), another one attached doesn't show up this
>> symptom. The partition table is OK (dangerous dedicated on both
>> drives, LBA mode set in the BIOS; fdisk/BIOS/in core disklabel agree).
>> I use flags 0x80ff for both drives (32-bit multiple (16) sector mode).
>> shutdown of the system seems to write all dirty blocks ("5 3 2 done")
>
>This is generally attributable to IDE.
>
>To see if your problem is real or imaginary, after fsck'ing the
>drive once (while mounted read-only), do it again.
>
>If you get the same thing (i.e., a drive doesn't stay fsck'ed
>when it should), then this is your problem.
No, only the 1st fsck shows up this error. (Today the error isn't 100%
reproducible. I was able to get some reboots without the fs errors)

>
>
>To resolve this problem, use as short an IDE cable as you possibly can;
>IDE is particularly sensitive to electrical interference, and requires
>short cables in the standard for this reason.
Tried it all:
The IDE cable is no longer than 20-30 cm. I even disabled 32 bit mode and
multiple sector mode for the wdc driver (flags 0), disabled UDMA support
and set PIO mode 0 in the BIOS (performance is now down to 2.2 MB/s).
Still the same errors. (It's a standard P-II LX board, nothing special, the
other drive, running at PIO mode 3 on a much longer cable, doesn't show up
this behaviour)

>Since EIDE is just IDE rehashed and given a facelift, this
>applies to EIDE as well.
>
>
>Note that you may actually be doing bad things to your disk contents
>with each fsck; it depends on just how noisy things are.  Your best
>bet would be to get a shorer cable, back it up *now*, and then after
>reinstalling, restore from backup.
What really wonders me that only the superblock seems to get hosed. I did
several "make world" before and didn't get any errors. I suspect something
really weird happens during the shutdown process, but I don't know what.
The superblock seems to get written to disk, otherwise the fs state wouldn't
be clean.
Where does df (or fsstat) get the number of free blocks/inodes (df shows
plenty of them) and where does the ffs allocator get them.
- fsck *only* tells me "SUMMARY INFORMATION BAD", nothing more, nothing less.
- df -ki shows plenty of free blocks/inodes
- If I delete files/blocks on the disk I am able to fill them again up, e.g.
  if I delete 10 files, I am able to recreate 10 files, if I truncate a file
  I am able to lengthen it again. Modifying files (without changing the
  length of them) also works as expected.

I will now try to disable any APM modes in the BIOS and kernel and test
again.

Daniel

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