On 4/26/2010 11:57 AM, Tim Clewlow wrote:
I'm afraid that opinions of RAID vary widely on this list (no surprise) but you may be interested to note that we agree (a consensus) that software-RAID 6 is an unfortunate choice.. Is this for performance reasons or potential data loss. I can live with slow writes, reads should not be all that affected, but data loss is something I'd really like to avoid. Regards, Tim.
Performance.RAID 6 (and 5) perform well when less than approximately 1/3 full. After that, even reads suffer. True hardware RAID can compensate somewhat, but you are contemplating mdraid. Data loss should not be an issue if your array can rebuild fast enough. RAID 6 can usually withstand the loss of two drives.
I like RAID 10, but I'm considered peculiar. RAID 10 can often withstand the loss of two drives (but not always) and performs a bit better, with much more graceful degradation of performance as the volume fills up. It performs reasonably well 2/3 full.
If data loss is crucial, RAIDed arrays can always lose one drive and recover, but for very important data, mirrors (RAID 1) are better. Put four drives in a RAID 1, you can suffer a loss of three drives.
MAA