Hello All,
I'm building a new Linux box, and I've decided to store the main portion of
the data in an LVM-on-raid10. I have three identical disks, partitioned as so:
hyperion ~ # sfdisk -lL -uM /dev/sdc
Disk /dev/sdc: 121601 cylinders, 255 heads, 63 sectors/track
Units = mebibytes of 1048576 bytes, blocks of 1024 bytes, counting from 0
Device Boot Start End MiB #blocks Id System
/dev/sdc1 * 0+ 94- 95- 96358+ fd Linux raid autodetect
/dev/sdc2 94+ 1066- 973- 996030 fd Linux raid autodetect
/dev/sdc3 1066+ 4973- 3907- 4000185 fd Linux raid autodetect
/dev/sdc4 4973+ 577179- 572206- 585938745 5 Extended
/dev/sdc5 4973+ 577179- 572206- 585938713+ fd Linux raid autodetect
The first three partitions are /boot, /, and swap. They're all raid1, and I'm
happy with them.
The confusion starts with the last partition. I created them in cfdisk as a
600000 MB (base 10, didn't realize that at the time) partition. I then created
a raid10 using the sd[abc]5 partitions:
mdadm --create /dev/md3 --level=10 --layout=f2 --raid-devices=3 /dev/sda5
/dev/sdb5 /dev/sdc5
After the re-sync finished, here's what /proc/mdstat has to say about it:
md3 : active raid10 sdc5[2] sdb5[1] sda5[0]
878907840 blocks 64K chunks 2 far-copies [3/3] [UUU]
And here's the detail:
hyperion ~ # mdadm --detail /dev/md3
/dev/md3:
Version : 00.90
Creation Time : Wed Oct 8 23:41:22 2008
Raid Level : raid10
Array Size : 878907840 (838.19 GiB 900.00 GB)
Used Dev Size : 585938560 (558.79 GiB 600.00 GB)
Raid Devices : 3
Total Devices : 3
Preferred Minor : 3
Persistence : Superblock is persistent
Update Time : Sat Oct 11 14:07:18 2008
State : clean
Active Devices : 3
Working Devices : 3
Failed Devices : 0
Spare Devices : 0
Layout : near=1, far=2
Chunk Size : 64K
UUID : b9141d0e:6beebd00:11e8198a:ff85a9d7
Events : 0.4
Number Major Minor RaidDevice State
0 8 5 0 active sync /dev/sda5
1 8 21 1 active sync /dev/sdb5
2 8 37 2 active sync /dev/sdc5
There are two things I don't understand here:
Why does the "Layout" line say "near=1, far=2"? Does that indicate that there
are three copies of every block? Even though I have three drives, I only
wanted two copies of each block.
Where's the rest of my space? I put 1800 GB (again, base 10) of space into the
array, but the total of "Array Size" and "Used Dev Size" is only 1500 GB.
Where's the other 300 GB? Was it lost to formatting?
A few last details: I'm running x86_64 kernel 2.6.26 compiled from gentoo-
sources-2.6.26-r1, and I have mdadm version 2.6.7.
I haven't moved any data to this array yet, so if I've done something daft, I
should be able to correct it easily, if you care to enlighten me. I'd also
appreciate any advice on any other place I could have found the answers to
these questions. My google searches weren't coming up with much.
Thank you,
Trebor
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
