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:

• Ubuntu RAID Tweak
• Linux RAID mdraid "stripe_cache_size" vs. transfer rate

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.

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).