RSYNC Fedora (Moving onto RAID...)

Scott Burns scott at
Wed Nov 26 06:20:27 UTC 2003

William Hooper wrote:

>Apples and oranges.  If you are going to compare multiple sets, why not
>compare 4 RAID5 sets w/ 3 disks each (12 in total).
You are right, in the apples and oranges.  What I took out of it was the 
opinion that while most people are happy with RAID5, it's the poor 
cousin where multiple drive failures are concerned.  Also, I get the 
impression (from my own experience) RAID5 tends to get pushed by 
salespeople because it is the cheapest RAID to implement.

>> If you lose 5/12 RAID10s you
>>still have over a 95% chance of no data lost.  I believe recovery time
>>on RAID10 puts RAID5 to shame too.  His entire rant can be found at
>He answers your question there:
>"Well with RAID10 there is no danger unless the one mirror that is
>recovering also fails and that's 80% or more less likely than that any
>other drive in a RAID5 array will fail!"
I'm not sure how he figured this number.  I do know that when I figured 
some numbers out for myself I used 3x4 rather than 2x4 like he did.

>Of course, he falls into the same trap you did, comparing a single RAID5
>set with multiple RAID10 sets.
Unless my terminology is wrong, it's only one RAID10 set, that is, 
multiple RAID1 sets making up a RAID0 stripe. RAID1+0 as I think some 
people call it.

However, you are right in that there is no reason you can't make it a 
RAID1+5 with 10 disks or even 15 disks to give the same sorts of 
protection or better than the 12 disk RAID10.  I take the rant along the 
lines of "if you're going to the trouble, go with the best you can, and 
RAID5 isn't it".  This is why I'm interested in why other's have RAID 
failures and what they plan(ned) to do next.

Scott Burns
Mirrabooka Systems

Tel +61 7 3857 7899
Fax +61 7 3857 1368 

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