Christopher Chan wrote: > Ross S. W. Walker wrote: > > 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. > > Here we go. Please go and hammer Neil Brown about his version of RAID10 > for md which is decidedly different from doing md 0+1/1+0. > http://neil.brown.name/blog/20040827225440 Well I don't want to hammer Neil and his RAID implementation, but technically, it isn't really RAID10, really Neil has come up with a whole new RAID level on to itself. It's quite good, don't get me wrong, it's just not RAID10. > Feel free to also hammer him on his definition of raid 1+0/0+1 as he > calls raid 0+1 "a raid0 array built over a collection of > raid1 arrays". Well I am not going to hammer him on that either. In fact I am not out to "hammer" anybody here. We are professionals here not children. > > 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. > > A failure of one mirror will destroy the whole raid 1+0 array too. I do > not see how having a functional raid0 array on one side of the mirror in > raid 0+1 will cut writes to one disk instead of two. How about a quick picture, O = good disk, X = failed disk, Stripe of mirrors: X O X -|-|- O X O A mirror of stripes: X|O|O ----- O|X|O So on the first as only 1 disk in each mirror was affected the RAID array as a whole survives, but on the second since both sides have a total loss the array as a whole fails. > However, I would personally go for a stripe of mirrored disks since a > rebuild will not involve all disks. Another good point I forgot to mention. > > 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. > > Yes, any hardware raid doing raid5 without a decent amount of cache is > going to be very poor on write performance. > > > > > 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). > > Next time, please follow the thread. We are japping about the raid10 > module for md by Neil Brown and how it apparently does not require the > traditional way of doing raid 1+0/0+1. Like how his module can do > "raid10" with just three disks. > > http://neil.brown.name/blog/20040827225440 My Apologies I thought the thread was "RAID5 or RAID50 for database?". I will next time look out for the hijacking and take appropriate action. > > 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. > > > > Thank you for your information. Your welcome. -Ross ______________________________________________________________________ This e-mail, and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail, you are hereby notified that any dissemination, distribution or copying of this e-mail, and any attachments thereto, is strictly prohibited. If you have received this e-mail in error, please immediately notify the sender and permanently delete the original and any copy or printout thereof.