Hi Neil, et al...
(btw: do we have an issue tracker somewhere?)
I was experimenting a bit... created two GPT partitions exactly 10 GiB
(aka 20971520 sectors a 512B).
Created a raid 1 on them:
mdadm --create /dev/md/data --verbose --metadata=1.2 --raid-devices=2
--spare-devices=0 --size=max --chunk=32 --level=raid1 --bitmap=internal
--name=data /dev/sda1 /dev/sdb1
The size is a multiple of the 32KiB so no rounding effects should kick
in.
Now:
--examine gives for both devices:
Avail Dev Size : 20969472 (10.00 GiB 10.74 GB)
Array Size : 20969328 (10.00 GiB 10.74 GB)
Used Dev Size : 20969328 (10.00 GiB 10.74 GB)
Data Offset : 2048 sectors
Super Offset : 8 sectors
=> Avail is the available payload size on each component device,... so
given that we have the first 2048S for the superblock/bitmap/etc... that
fits exactly.
=> Why is the array size / used dev size smaller?
--detail gives:
Array Size : 10484664 (10.00 GiB 10.74 GB)
Used Dev Size : 10484664 (10.00 GiB 10.74 GB)
=> That's half of the Array Size from above? Is that a bug?
--query gives even another value:
/dev/md/data: 9.100GiB raid1 2 devices, 0 spares. Use mdadm --detail for
more detail.
=> But the device really has 20969328S it seems... so the 9.1 GiB seems
a bit bogus as well?
Last but not least... when the tools print values like "10.00 GiB 10.74
GB"... wouldn't it be better if they printed "~10.00 GiB ~10.74 GB" or
something like this to show that the values are rounded and not
_exactly_ 10 GiB... could be helpful to avoid misalignment issues.
Cheers,
Chris.
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