[Stgt-devel] stgt and large devices?

Tomasz Chmielewski mangoo
Wed May 16 12:15:12 CEST 2007

Bastian Blank schrieb:
> On Tue, May 15, 2007 at 04:35:11PM +0200, Tomasz Chmielewski wrote:
>> when I browse through the beginning of a disk, I can see some familiar 
>> content, but it is nevertheless different.
> Are you able to describe the differences?

Well, it's hard to describe the difference in binary data.

First, I did a "dd" of a first 10 MB of the disk or so, for IET and 
tgtd, compared md5sums - different.

Which shouldn't happen, as I didn't even mount the disks.

Then, I opened the files I created with dd in an editor - totally 
different, not just a couple of bytes here and there.

So let's make an experiment: create a 10 MB file out of /etc/services 
(basically, "cat" it several times after each other, until the text 
document has 10 MB).

Then, do (part - disk available via iSCSI):


# dd if=/services-big of=part
# dd if=part of=/part.iet bs=1k count=10000

When inspected with hexedit, we see text/services file.


# dd if=part of=/part.tgtd bs=1k count=10000

When inspected with hexedit, file is different.

# diff -u part.iet part.tgtd > part.diff

It resulted in a 600 kB diff file.

Whereas part.iet begins as /etc/services file, part.tgtd doesn't - it 
starts like that:

rror interpretation service
afs3-errors     7006/udp                        # error interpretation 
afs3-bos        7007/tcp                        # basic overseer process

It begins 1630 lines later.

# dd if=part of=/part.tgtd2 bs=1k count=10000
# dd if=part of=/part.tgtd3 bs=1k count=10000

# md5sum /part.*
bf38437967c33219c1852d0000b3e593  /part.tgtd2
c4a9207d7fb97f645b4b30142874d3fd  /part.tgtd3

# diff -u /part.tgtd2 /part.tgtd3 > /part-gt.diff

# ls -l /part-gt.diff
-rw-r--r-- 1 root root 218099 May 16 12:11 /part-gt.diff

Generally, the data seems *almost* intact, but the order is incorrect etc.

So I have two observations:

- it doesn't happen on x86
- it happens on ARM
- it doesn't depend on size of the device as I though at the beginning

Tomasz Chmielewski

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