mdadm RAID creation

Here comes the fun part!! Let's create the RAID...

A good read on partition alignment.

chunk size = stripe size = minimum size that can be written to the disk

I wil use parted for the for the partitioning and alignment. Do the following for each drive.

sudo parted -a optimal /dev/sdi (parted) mklabel gpt Warning: The existing disk label on /dev/sdi will be destroyed and all data on this disk will be lost. Do you want to continue? Yes/No? Yes (parted) mkpart Partition name? []? File system type? [ext2]? ext4 Start? 2048s End? -1 (parted) set 1 raid on (parted) align-check opt 1 1 aligned (parted) print Model: ATA WDC WD20EARS-00J (scsi) Disk /dev/sdi: 2000GB Sector size (logical/physical): 512B/512B Partition Table: gpt Number Start End Size File system Name Flags 1 1049kB 2000GB 2000GB raid

And here we go:

mdadm --create /dev/md0 --verbose --level=5 --metadata=1.2 --raid-devices=5 /dev/sda1 /dev/sdc1 /dev/sdd1 /dev/sdg1 /dev/sdi1
The RAID array starts in degraded mode with a spare drive. The spare drive is added to the array at the end and the array can then perform at full speed

cat /proc/mdstat Personalities : [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid1] [raid10] md0 : active raid5 sdd1[5] sdg1[3] sdc1[2] sda1[1] sdi1[0] 7813527552 blocks super 1.2 level 5, 512k chunk, algorithm 2 [5/4] [UUUU_] [=>...................] recovery = 5.3% (105373832/1952992768) finish=359.9min speed=85546K/sec

and then we create the new partition on the newly created device

'stride' is the amount of data written to each disk and 'stripe width' is the stride length * number of active drives. 4 in my case as the fifth drive is a parity drive. There are many calculators available, just google for on.

sudo mkfs.ext4 -b 4096 -E stride=128,stripe-width=512 /dev/md0 mke2fs 1.42 (29-Nov-2011) Filesystem label= OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) Stride=128 blocks, Stripe width=512 blocks 244174848 inodes, 1953381888 blocks 97669094 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=0 59613 block groups 32768 blocks per group, 32768 fragments per group 4096 inodes per group Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968, 102400000, 214990848, 512000000, 550731776, 644972544, 1934917632 Allocating group tables: done Writing inode tables: done Creating journal (32768 blocks): done Writing superblocks and filesystem accounting information: done
Remember to add the new device in fstab if you would like it to be mounted automatically.

sudo blkid /dev/md0 /dev/md0: UUID="25b9807c-d7f0-4e5e-98d3-0209a1d58f6c" TYPE="ext4"

add this line to /etc/fstab in my case:

UUID="25b9807c-d7f0-4e5e-98d3-0209a1d58f6c" /Storage/ ext4 defaults 0 0