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5. Usage

5.1 fdisk, mke2fs, mount, etc.

You can now start treating the RAID as a regular disk. The first thing you'll need to do is partition the disk (using fdisk). You'll then need to set up an ext2 filesystem. This can be done by running the command:

% mkfs -t ext2 /dev/sdxN

where /dev/sdxN is the name of the SCSI partition. Once you do this, you'll be able to mount the partitions and use them as you would any other disk (including adding entries in /etc/fstab).

5.2 Hotswapping

We first tried to test hotswapping by removing a drive and putting it back in the DPT-supplied enclosure/tower (which you buy for an additional cost). Before we could carry this out to completion, one of the disks failed (as I write this, the beeping is driving me crazy). Even though one of the disks failed, all the data on the RAID drive is accessible.

Instead of replacing the drive, we just went through the motions and put the same drive back in. The drive rebuilt itself and everything seems to be okay. During the time the disk had filed, and during the rebuilding process, all the data was accessible. Though it should be noted that if another disk had failed, we'd have been in serious trouble.

5.3 Performance

Here's the output of the Bonnie program, on a 2144 UW with 9x3=17 GB RAID 5 setup. The RAID is on a dual processor Pentium Pro machine running Linux 2.0.32. For comparison, the Bonnie results for the IDE drive on that machine are also given.

           -------Sequential Output-------- ---Sequential Input--  --Random--            
           -Per Char- --Block--- -Rewrite-- -Per Char- --Block---  --Seeks---            
        MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU   /sec  %CPU 
RAID   100  9210 96.8  1613  5.9   717  5.8  3797 36.1 90931 96.8 4648.2 159.2 
IDE    100  3277 32.0  6325 23.5  2627 18.3  4818 44.8 59697 88.0  575.9  16.3

It's clear that the RAID is great for block reads and writes (even though write performance is degraded by using RAID-5), but it is not very good at sequential re-writes.

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