Christopher Chan wrote:
William Warren wrote:
I'm not a fan of RAID 5 at all since it can only tolerate one failure at all. Go with raid 10 or something like that which is able to handle more than one failure. Intermittent, uncorrectable sector failures during rebuilds are becoming an increasing problem with today's drives.
Is that raid10 or raid 1+0 or raid 0+1? :D
At least for the latter two, their handling more than one failure depends on which disks blow. Not sure how the raid10 module handles things.
Whoever implements RAID10 will want the RAID1+0 which is a stripe set of mirrors, rather then the RAID0+1 which is a mirror of stripe sets.
The problem being two fold, 1) in a RAID0+1 a single drive failure on either side of the mirror will put the whole array into total failure jeopardy, a failure on both sides is a total loss, 2) the pathway for simultaneous operations is cut down from (say X is an even number of disks) X reads, X/2 writes, to 2 reads, 1 write.
On a RAID5/6 array you are limited to a pathway of 1 read and 1 write at a time and all writes must write across the entire stripe, so if you do choose RAID5/6 then it is highly recommended to use a hardware RAID controller with a BBU write-back and read-ahead cache which can minimize the impact of this by caching a whole stripe set to write at once and to have a stripe set of reads waiting for io requests.
For database log files and other applications that do a lot of random io it is recommended to use fast RPM drives in a RAID10 which has the multiple pathways for reads and writes which will maximize the total number of random IOPS (ios per second).
Typically most vendors recommend a two-prong approach, keep the database data files on a RAID5/RAID6 type array and keep the log files on a RAID10 array.
-Ross
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