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SubjectPROBLEM: silent data corruption using HPT370 on an ABIT VP6
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1. Silent disk corruption using HPT370 on an ABIT VP6

2. I have tracked down a crooked bug somewhere in the IDE driver
leading to a slow and silent data corruption, which is a most alarming threat
for the incautious. The case is simple: "cp file1 file2; diff file1 file2"
shows differences under certain conditions.

3. Keywords: kernel, driver, ide, data corruption, i386

4. Kernel versions: 2.4.16 or 2.4.18 (error reproducible in both versions)

5. Hardware environment (details see below):
ABIT VP6 motherboard including: dual Pentium III, VIA APOLLO PRO chipset
VIA onboard EIDE controller,
HPT370 "raid" UDMA/100 controller, integrated on board
Promise TX2 (PDC) UDMA/100 PCI controller card
Hard disks (all masters):
2 x 6GB Quantum Fireball EX6.4A on VIA,
2 x 40GB Quantum FireballP AS40.0 on PDC,
2 x 40GB Quantum FireballP AS40.0 on HPT

6. Software environment:
IDE driver (kernel-integrated)
raidtools-0.90-5 (optional)
General: four 40GB disks of identical geometry have three partitions each,
same partitioning, identified by /dev/hd[e,g,i,k][1-3],
/dev/md[0-2} are three RAID-5 arrays defined on the four disks accordingly
each out of three raid partitions are formatted ext3 with internal journal

7. ERROR description:
Let "file1" be a "large" data file, e.g. 1GB, on a RAID array described above.
Then "cp file1 file2; cmp -l file1 file2" shows (subtle) differences.
There are random differences on several random spots between the files.
The "spots" occur usually as blocks of few bytes in succession. The difference
is up to several dozens of bytes at a 1GB file copy.

8. Tracking down the error:
I have conducted over 100 test cases: the error is consistent, though random.

First I excluded an error in the raid software:
umount /dev/md[0-2]; raidstop /dev/md[0-2].
I used a script to read all four raw disks concurrent:

for d in e, g, i, k; do \
(for i in 1 2 3 4 5; do \
dd if=/dev/hd"$d"1 count=2500000 \
2> /dev/null | md5sum; done \
) >> trc"$d".md5sum done

I found NO differences in trce.md5sum and trcg.md5sum (both disks are on the
Promise controller), but significant differences in trci.md5sum and trck.md5sum,
displaying 3 and 5 different read results out of 5 identical reads, resp.
(both disks are on the HPT370 controller).

Oops!!!

I stayed focused on the HPT370 controller, and compiled a small test environment with a
single processor motherboard and a HPT370A PCI controller card, which, in addition, has
the same HPT BIOS version (1.0.3b1) as the integrated one. I found no problem using this
configuration, so the error might well be related only to the SMP architecture.

9. Solution or workaround?
I browsed through the HighPoint Software web pages and found a remarkable replacement
for the kernel IDE-driver. This is a SCSI IDE emulation module, called hpt37x2.o, that
can be built for "any" 2.4.x kernel. And IT WORKS, at least for me, since at least two days ;)
The only drawback is, that it is not GPL-d and the complete source is not available.
The existence of a working driver is a profound proof for the kernel driver to be in error!

10. Attachments:
I have saved several files out of /proc, boot log, etc. from the test period,
i.e. by using the faulty driver. They are available upon request. Due to the fact, that the
HPT driver is not a native IDE-driver, but a SCSI-emulation, it is not possible to switch
between booting the old and new kernels very easily. One example, the raid arrays are not
recognised from the foreign configuration.

Peter Breuer [P.Breuer@freemail.hu]


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