Hi Anton,
On Wed, Apr 8, 2009 at 1:34 AM, Anton Ertl <[email protected]
> wrote:
> I have released a new version of hdtest, a program that tests whether
> hard disks write out-of-order relative to the order that the writes
> were passed to them from the OS. You find the program at
>
> http://www.complang.tuwien.ac.at/anton/hdtest/
I would like to to give a try to your program. If i find it useful, i would
like to absorb it inside the Linux Test Project (LTP). Would you be willing
to share this test program then with us under GPL ?
Regards--
Subrata
http://ltp.sourceforge.net/,
<http://www.complang.tuwien.ac.at/anton/hdtest/>
>
> Here I mainly present the results from my tests, and explain enough
> about the program so you know what I am talking about.
>
>
> HOW DOES IT WORK?
>
> It writes the blocks in an order like this:
>
> 1000-0-1001-0-1002-0-...
>
> This sequence seems to inspire PATA and SATA disks to write
> out-of-order (in the order 1000-1001-1002-...-0). So you turn off the
> drive's power while running the program. The written blocks contain
> certain data that another program from the suite can check after you
> power the drive up again.
>
>
> RESULTS
>
> I performed two sets of tests, one in November 1999, and one in April
> 2009. The results have not changed much. In both tests disks wrote
> data seriously out-of-order in their default configuration; they can
> delay the writing of block 0 in this test for quite a long time.
>
> In more detail:
>
> In 2009 I tested three drives (and accessed the whole drive) under
> Linux 2.6.18 on Debian Etch; the USB enclosure used was a Tsunami
> Elegant 3.5" Enclosure that has PATA and SATA disk drive interfaces.
>
> * Maxtor L300R0 PATA (300GB) connected through an USB enclosure: In
> two tests it wrote the consecutive blocks 47 and 34 blocks after the
> last written block 0.
>
> * Seagate ST340062 Model 0A PATA (7200.10, 400GB):
> connected through a USB enclosure:
> 3 times the result was as if it had written the blocks in-order
> 1 time it wrote 3064 blocks out-of-order
> 2 times it wrote 18384 blocks out-of-order
> connected directly via PATA cable:
> 1 time it wrote 1972 blocks out-of-order
>
> * Seagate ST340062 Model 0AS SATA (7200.10, 400GB) connected through a
> USB enclosure:
> 1 time the result was as if it had written the blocks in-order
> 2 times it wrote 3064 blocks out-of-order
> 1 time it wrote 6128 blocks out-of-order
> 1 time it wrote 12256 blocks out-of-order
> 1 time it did not write block 0 at all
>
> It is interesting that the number of blocks that is found to be
> out-of-order is often a multiple of 3064. Maybe this is a multiple of
> a track size; no other explanations come to mind.
>
> In 1999 I tested two drives (and accessed one partition) under
> Linux-2.2.1 on RedHat 5.1. The two drives were a Quantum Fireball
> CR8.4A (8GB) and an IBM-DHEA-36480 (6GB), both connected directly via
> PATA. I did one test with each of the disks, and they did not even
> write block 0 once on the platters before I turned off the power.
>
> I also tested the Quantum with write caching disabled (hdparm -W 0).
> Hdtest was now quite noisy and produced the in-order result.
>
>
> CONCLUSION
>
> Applications and file systems requiring in-order writes (i.e.,
> basically all of them) should use barriers or turn off write caching
> for the disk drive(s) they use. Unfortunately, the Linux ext3 file
> system does not use barriers by default; use the mount option
> barrier=1 to enable them, e.g. by putting a line like this in
> /etc/fstab:
>
> /dev/md2 /home ext3 defaults,barrier=1 1 2
>
> - anton
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--
Regards & Thanks--
Subrata
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