My home partition hit 90% recently and I decided it was time to upgrade my storage. I had been running 4x250GB hard disks in a RAID1/RAID10 setup and switched to a 2x1TB RAID1 setup. The drives were Western Digital Advanced Format drives with 4kB physical sectors and 512B logical sectors. It is important when partitioning these drives to ensure that partitions start on a logical sector number that is divisible by 8 otherwise performance will suffer as file system clusters will not be aligned to the underlying 4kB physical sector. If the partition is not aligned then writes turn into a read-modify-write. I also decided to use a GPT instead of an MBR partition table. I used gdisk to create boot, swap, root and home partitions:
$ sudo sgdisk -p /dev/sda Disk /dev/sda: 1953525168 sectors, 931.5 GiB Logical sector size: 512 bytes Disk identifier (GUID): 0658FE0C-AE06-4FD9-8CCC-7DDB178BB0CA Partition table holds up to 128 entries First usable sector is 34, last usable sector is 1953525134 Partitions will be aligned on 2048-sector boundaries Total free space is 3437 sectors (1.7 MiB) Number Start (sector) End (sector) Size Code Name 1 2048 264191 128.0 MiB FD00 Linux RAID 2 264192 12847103 6.0 GiB 8200 Linux swap 3 12847104 147064831 64.0 GiB FD00 Linux RAID 4 147064832 1953523711 861.4 GiB FD00 Linux RAID
I actually aligned the start of all my partitions to 1MiB (2048 sectors) which seems to be somewhat of an industry standard and was suggested by gdisk as well.
I had done some research into how to exactly boot Linux on a GPT disk and was happy to find that my boot loader, extlinux, works out of the box. Installing extlinux was as simple as:
# extlinux --raid --install /boot/extlinux # sgdisk /dev/sda --attributes=1:set:2 # sgdisk /dev/sdb --attributes=1:set:2 # cat /usr/lib/syslinux/gptmbr.bin > /dev/sda # cat /usr/lib/syslinux/gptmbr.bin > /dev/sdb
These commands install ldlinux.sys, set the bootable attribute for partition 1 of both disks and install the gptmbr.bin boot code into the first sector of both disks.
Once my file systems were copied onto my new disk setup I recreated my initrd images with a new /etc/mdadm.conf and edited /etc/fstab and /boot/extlinux/extlinux.conf. The Arch Linux Wiki article Installing with Software RAID or LVM proved handy for assembling the arrays.
I now have plenty of disk space again:
$ pydf / /boot /home Filesystem Size Used Avail Use% Mounted on /dev/md1 63G 31G 29G 48.6 [#############..............] / /dev/md0 124M 17M 101M 13.6 [####.......................] /boot /dev/md2 861G 373G 488G 43.3 [############...............] /home
A quick check with Bonnie++ showed that disk performance was as expected which confirmed that I hadn't made any mistakes with partition alignment.