[PLUG] missing space on RAID-0 volume

[bergman@merctech.com]

Hello,

I've got a RAID-0 volume (yes, I know the implications re. data loss), and it 
seems to be smaller than it should be.

The physical disks are 2x80GB (actually, 2x74.5GB, for powers of 1024b, not
marketing-GB w. powers of 1000). There's ~7.5GB taken from /dev/sda to create /
(4GB) and swap (3.5GB). The md driver is supposed to be able to create RAID0
volumes that are pure concatenations--ie., volumes of different sizes simply
added together.

-------------------------------------
	Disk /dev/sda: 80.0 GB, 80000000000 bytes
	255 heads, 63 sectors/track, 9726 cylinders
	Units = cylinders of 16065 * 512 = 8225280 bytes

	Disk /dev/sdb: 80.0 GB, 80000000000 bytes
	255 heads, 63 sectors/track, 9726 cylinders
	Units = cylinders of 16065 * 512 = 8225280 bytes
-------------------------------------


The /dev/md0 volume is composed of two partitions:

   Device Boot    Start       End    Blocks   Id  System
/dev/sda3           914      9726  70790422+  fd  Linux raid autodetect
/dev/sdb1   *         1      9726  78124063+  fd  Linux raid autodetect

So, the total should be 148914485 blocks. Actually, tune2fs reports that the 
md0 device has 148914177 1KB blocks (an insignificant difference of 308 blocks).
The ext3fs filesystem is configured with 1% reserved, so there should be 
147425036 1K blocks in the filesystem (140.595GB).

[On a side note, running "fdisk -l /dev/md0" reports that the RAID0 device is 
142GB, which is almost exactly what I'd expect, but I don't know how meaningful 
it is to use fdisk to examine a meta-device "disk".]

However, the "df" size of the RAID0 volume is 130251578 1K blocks (124.21GB).

So...where's the missing ~16GB? I can't believe that the md driver has an 
overhead of more than 10%.

Any ideas?


Environment:
	Red Hat Enterprise Linux ES release 3 (Taroon Update 5)
	mdadm-1.5.0-9
	raidtools-1.00.3-8.EL3
	e2fsprogs-1.32-15.1

Thanks,

Mark

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