[dm-devel] Why it can not support more than 100 targets in 1 MD ?

[Ji Haitao]

Hello,

Sorry for my poor English. I'm having trouble with device-mapper and 
need your help.

I create a MD having 100 targets with dmsetup. IO error occurs when I 
access the 100th target. My operation steps are :

1.#create md
sh> dmsetup create vd1 dmtable1

2.
#access the 100th target
sh> dd bs=512 count=10 if=/dev/zero of=/dev/mapper/vd1 seek=51380224

#errors happen
dd: writing `/dev/mapper/vd1': Input/output error
1+0 records in
0+0 records out

If I only have 99 targets in dmtable1, everything is OK when I access 
the 99th target. Why? If device-mapper can support more than 100 targets 
in 1 MD ?

The content of dmtable1 is:
0 524288 linear /dev/hdb4 0
524288 524288 linear /dev/hdb4 0
1048576 524288 linear /dev/hdb4 0
1572864 524288 linear /dev/hdb4 0
2097152 524288 linear /dev/hdb4 0
2621440 524288 linear /dev/hdb4 0
3145728 524288 linear /dev/hdb4 0
3670016 524288 linear /dev/hdb4 0
4194304 524288 linear /dev/hdb4 0
4718592 524288 linear /dev/hdb4 0
5242880 524288 linear /dev/hdb4 0
5767168 524288 linear /dev/hdb4 0
6291456 524288 linear /dev/hdb4 0
6815744 524288 linear /dev/hdb4 0
7340032 524288 linear /dev/hdb4 0
7864320 524288 linear /dev/hdb4 0
8388608 524288 linear /dev/hdb4 0
8912896 524288 linear /dev/hdb4 0
9437184 524288 linear /dev/hdb4 0
9961472 524288 linear /dev/hdb4 0
10485760 524288 linear /dev/hdb4 0
11010048 524288 linear /dev/hdb4 0
11534336 524288 linear /dev/hdb4 0
12058624 524288 linear /dev/hdb4 0
12582912 524288 linear /dev/hdb4 0
13107200 524288 linear /dev/hdb4 0
13631488 524288 linear /dev/hdb4 0
14155776 524288 linear /dev/hdb4 0
14680064 524288 linear /dev/hdb4 0
15204352 524288 linear /dev/hdb4 0
15728640 524288 linear /dev/hdb4 0
16252928 524288 linear /dev/hdb4 0
16777216 524288 linear /dev/hdb4 0
17301504 524288 linear /dev/hdb4 0
17825792 524288 linear /dev/hdb4 0
18350080 524288 linear /dev/hdb4 0
18874368 524288 linear /dev/hdb4 0
19398656 524288 linear /dev/hdb4 0
19922944 524288 linear /dev/hdb4 0
20447232 524288 linear /dev/hdb4 0
20971520 524288 linear /dev/hdb4 0
21495808 524288 linear /dev/hdb4 0
22020096 524288 linear /dev/hdb4 0
22544384 524288 linear /dev/hdb4 0
23068672 524288 linear /dev/hdb4 0
23592960 524288 linear /dev/hdb4 0
24117248 524288 linear /dev/hdb4 0
24641536 524288 linear /dev/hdb4 0
25165824 524288 linear /dev/hdb4 0
25690112 524288 linear /dev/hdb4 0
26214400 524288 linear /dev/hdb4 0
26738688 524288 linear /dev/hdb4 0
27262976 524288 linear /dev/hdb4 0
27787264 524288 linear /dev/hdb4 0
28311552 524288 linear /dev/hdb4 0
28835840 524288 linear /dev/hdb4 0
29360128 524288 linear /dev/hdb4 0
29884416 524288 linear /dev/hdb4 0
30408704 524288 linear /dev/hdb4 0
30932992 524288 linear /dev/hdb4 0
31457280 524288 linear /dev/hdb4 0
31981568 524288 linear /dev/hdb4 0
32505856 524288 linear /dev/hdb4 0
33030144 524288 linear /dev/hdb4 0
33554432 524288 linear /dev/hdb4 0
34078720 524288 linear /dev/hdb4 0
34603008 524288 linear /dev/hdb4 0
35127296 524288 linear /dev/hdb4 0
35651584 524288 linear /dev/hdb4 0
36175872 524288 linear /dev/hdb4 0
36700160 524288 linear /dev/hdb4 0
37224448 524288 linear /dev/hdb4 0
37748736 524288 linear /dev/hdb4 0
38273024 524288 linear /dev/hdb4 0
38797312 524288 linear /dev/hdb4 0
39321600 524288 linear /dev/hdb4 0
39845888 524288 linear /dev/hdb4 0
40370176 524288 linear /dev/hdb4 0
40894464 524288 linear /dev/hdb4 0
41418752 524288 linear /dev/hdb4 0
41943040 524288 linear /dev/hdb4 0
42467328 524288 linear /dev/hdb4 0
42991616 524288 linear /dev/hdb4 0
43515904 524288 linear /dev/hdb4 0
44040192 524288 linear /dev/hdb4 0
44564480 524288 linear /dev/hdb4 0
45088768 524288 linear /dev/hdb4 0
45613056 524288 linear /dev/hdb4 0
46137344 524288 linear /dev/hdb4 0
46661632 524288 linear /dev/hdb4 0
47185920 524288 linear /dev/hdb4 0
47710208 524288 linear /dev/hdb4 0
48234496 524288 linear /dev/hdb4 0
48758784 524288 linear /dev/hdb4 0
49283072 524288 linear /dev/hdb4 0
49807360 524288 linear /dev/hdb4 0
50331648 524288 linear /dev/hdb4 0
50855936 524288 linear /dev/hdb4 0
51380224 524288 linear /dev/hdb4 0
51904512 524288 linear /dev/hdb4 0

The configuration of my Linux host is:
CPU: P4 1.4G
MEM: 512M
Kernel: 2.4.21
device-mapper.1.00.05
dd (fileutils) 4.1.9

Thanks,
Ji Haitao