/dev/sda2 10G swap
/dev/sda3 (rest of the drive ~940G) /home
Then same with /dev/sdb
/dev/sdb1 50G /
/dev/sdb2 10G swap
/dev/sdb3 ~940G /home
then used the installer to configure software RAID-1 like that:
/dev/sda1 + /dev/sdb1 -> /dev/md0
/dev/sda2 + /dev/sdb2 -> /dev/md1
/dev/sda3 + /dev/sdb3 -> /dev/md2
With that installation proceeded nicely and I have debian wheezy now installed. The problem is that after I logged in Gnome I see in Disk Utility, for all 3 RAID md devices:
WARNING: The partition is misaligned by 512 bytes. This may result in very poor performance. Repartitioning is suggested.
Now, when I check the partitions that we created during installation on the disk seem to actually be aligned properly with the offset of 2048 sectors (x 512 bytes = 1M?):
root@sonata:~# fdisk -l /dev/sda /dev/sdb
Disk /dev/sda: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders, total 1953525168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x00030b9a
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 97656831 48827392 fd Linux raid autodetect
/dev/sda2 97656832 117188607 9765888 fd Linux raid autodetect
/dev/sda3 117188608 1953523711 918167552 fd Linux raid autodetect
Disk /dev/sdb: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders, total 1953525168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x0006affd
Device Boot Start End Blocks Id System
/dev/sdb1 * 2048 97656831 48827392 fd Linux raid autodetect
/dev/sdb2 97656832 117188607 9765888 fd Linux raid autodetect
/dev/sdb3 117188608 1953523711 918167552 fd Linux raid autodetect
On the other hand, when I check the RAID-1 devices I get the misalignment:
root@sonata:~# fdisk -l /dev/md0 /dev/md1 /dev/md2
Disk /dev/md0: 50.0 GB, 49965563904 bytes
255 heads, 63 sectors/track, 6074 cylinders, total 97588992 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x000cfa3c
Device Boot Start End Blocks Id System
/dev/md0p1 * 63 97578809 48789373+ 83 Linux
Partition 1 does not start on physical sector boundary.
Disk /dev/md1: 9991 MB, 9991749632 bytes
255 heads, 63 sectors/track, 1214 cylinders, total 19515136 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x000e0613
Device Boot Start End Blocks Id System
/dev/md1p1 63 19502909 9751423+ 82 Linux swap / Solaris
Partition 1 does not start on physical sector boundary.
Disk /dev/md2: 940.1 GB, 940069158912 bytes
255 heads, 63 sectors/track, 114290 cylinders, total 1836072576 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x0001ead5
Device Boot Start End Blocks Id System
/dev/md2p1 63 1836068849 918034393+ 83 Linux
Partition 1 does not start on physical sector boundary.
Now, the questions :)
1. Should the /dev/md{0,1,2}p1 devices Start at 64 and not 63? Or some other cylinder number to be properly aligned? That would explain the exact 512 bytes misalignment (1 sector)?
2. How did that happen? The partitiions on the disk were properly aligned, the sda1 sda2 sda3 sdb1 sdb2 sdb3? If they were properly aligned why weren't md devices created with proper alignment?
3. How significant of a performance drag are we talking in this particular case?
4. What are my options right now? How do I fix it? Can I fix it without reinstalling Debian Wheezy again?
5. If I have to go through the process of reinstalling again using debian wheezy netinst.iso, what exactly (and how) I am supposed to choose to make sure that md0 Starts at 64 and NOT 63? I didn't see these options during the installation? Also, since the partitions on the disk have 1M offset, should the MD devices also have 1M offset? Or that 63 offset starts AFTER the 1M offset? What should the proper Start be for the MD device in this case then? 64? Or a larger number? Another 2048 (1M)?
Would appreciate any insight here :)
--
Sincerely yours,
Alexandru Cardaniuc