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vnx pool design
Hello i just read the pool best practice and i have some question:
In those best practice we can see for 10k/15k drives go with raid 5
but we also can see for disk larger than 1tb and large pool use raid 6.
So for the "new" 900gb and 1.2tb 10k drives the best practice is raid 5 or raid 6 (i mean it will take at least 24h to rebuild with the 900gb drives)
Same when do you consider a pool is large? 40 disks? 60? 100?
I mean today i have to build a pool of 25tb with 900gb 10k drives did i create 4 8+1 or 4 8+2 ?
Thanks
Aglidic
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July 24th, 2013 01:00
hello thanks for the answer.
The IOps it's not an issue here.
My concern is more about the security of the data i mean today i have 4 RG in my pool and if i loose only 1 RG i will losse my entire pool so 25Tb.
That's why i'm a little worried with 8+1.
Plus in the future is possible than the pool will grow. So if a doudble drive failure happen it can just be catastrophic.
Like i said to a colleague i'm ok to make 8+1 on 15k drives with little capacity (300/600). But with 900 Gb the rebuild time start to be really consequent.
SKT2
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July 24th, 2013 01:00
Are you planing to reserve additonal spares because of this new addions?
do you have the totoal IOPS requirement calculated for the application which will be hosted in this pool? Do you have the RD/Wr ratio expcted out of this application? Having this informatio will be helpful to make your RAID level decision. Tthe total IOPS done on the back end will be higher for R6 versus R5 ( specifically the one contributed by the writes). so may be 2*(4+1) may be an option instead of 1*(8+2) if you chose to. R6 is better in protection, but adds additional overheads.
The pool being large or small may not be concern unless you are planning for expanding the pool. Recommendationas far as i know is increase by 100%( same number of disks already in the pool.
dynamox
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July 24th, 2013 04:00
yes, it's going to be your call ..capacity versus failure domain. With my 600G drives i went with 4+1R5, if i had 900G drives i personally would consider R6 because just recently i experienced double drive failure with 5+1R5 1TB SATA drives (it was not a pool but a traditional RG) so i still have that bad taste of data loss in my mouth.