Tuning Ubuntu's software RAID

Recently I encountered an issue where the read/write performance of Ubuntu's software RAID configuration was relatively poor. Fortunately, others have encountered this problem and have documented a potential cause and solution here:

The short story is that Ubuntu uses some very conservative defaults for RAID caching. Whilst this may ensure reliable behavior across a range of hardware, it does mean that for many read/write performance will be lacklustre. The solution to this problem is to define a more aggressive caching options on any software RAID partitions that are in use.

Enable LVM on software-RAID during a Suse installation

If you have tried setting up LVM on top of a LVM-enabled software-RAID partition during a standard Suse installation you may have hit a brick wall where the installer tells you that there are no available LVM partitions. This is a bug in the installer, it looks as if the LVM setup tool only checks physical partitions for LVM labels and ignores software-RAID partitions that have LVM labels.

Steve Wray has pointed out that you can get this functionality to work by creating a small physical partition and giving it an LVM label. The LVM setup tool will see this partition and allow the configuration to continue quite happily with the software-RAID partitions available for use. I have not tested this but I think it is worth giving a spin as the data integrity of RAID-1 coupled with the flexibility of LVM is a compelling combination (though performance maybe an issue).

Linux software RAID housekeeping

I performed some operating system maintanence this morning with the resizing and recreation of a few software RAID disks. It did result in some downtime whilst the mirrors were rebuilt but it was only for 30 minutes which is not bad. Overall the operation went pretty smoothly and I found the following two references very useful: