I'm trying to help a user with a problem with their isw set. After
upgrading to Ubuntu 11.04 ( 1.0.0.rc16 ) it seems that their partition
extends beyond the end of the raid array. I'm looking at how isw
computes the array length and it seems to be wrong. It looks like
_cal_array_size() computes the length of the ( raid1 ) array by finding
the smallest component disk and subtracting some reserved blocks. This
does not seem to be correct. Relevant fields from the user's metadata:
0x0e8 disk[0].totalBlocks: 1953523055
0x118 disk[1].totalBlocks: 1953525168
0x148 isw_dev[0].SizeLow: 1953519616
0x1ac isw_dev[0].vol.map[0].blocks_per_member: 1953519880
0x1b0 isw_dev[0].vol.map[0].num_data_stripes: 7630936
0x1b4 isw_dev[0].vol.map[0].blocks_per_strip: 128
Further, it looks like create_rd() sets the size of each component disk
to the same thing anyhow:
if ((r->sectors = dev->vol.map[0].blocks_per_member - RAID_DS_JOURNAL))
This seems to have given the user a block device with a total size of
1953519880 sectors. Debian and Ubuntu are carrying a patch that removes
the subtraction of RAID_DS_JOURNAL above, or the array would be even
smaller. This seems to have been added because a Debian user had a
similar shrinkage of their disk after an upgrade. As you can see, the
array size seems to be exactly equal to blocks_per_member, even though
_cal_array_size() appears to be subtracting DISK_RESERVED_BLOCKS, which
should make it a few hundred sectors smaller. I am not sure why this is.
I believe that the array size should be correctly computed as
blocks_per_strip * num_data_stripes. That appears to be off by a factor
of two however, so maybe blocks_per_strip is actually in kb instead of
sectors? Correcting for that gives an array length of 1953519616
sectors. This matches isw_dev[0].SizeLow. Perhaps this field should be
used directly since it gives the correct size, instead of doing any
calculations?
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