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In Reply to: Re: RAID Array ? posted by Rod M on May 11, 2007 at 08:49:45:
An even more fault tolerant flavor is RAID 10 (really 1+0). Here multiple RAID 1 drives are all mirrored. In this case, however, it would require eight drives. 4 data + 4 mirrors. You can lose half the array (so long as you don't lose both a primary and its mirror) and it still runs.Another advantage to RAID 10 is that the drives don't have to be striped. You can run the OS on one drive pair and the data on the others. In that way, even if there is a total failure, you don't necessarily lose both the OS and the data.
Follow Ups:
"Another advantage to RAID 10 is that the drives don't have to be striped."I think you lost me. Wouldn't that make it RAID 1? RAID 0 means a stripe is involved, right?
"You can run the OS on one drive pair and the data on the others. In that way, even if there is a total failure, you don't necessarily lose both the OS and the data."
True.
So basically, you're running RAID 1 for the 2 boot disks and RAID 1 for the two data disks.
You are thinking about RAID 0+1, which like RAID 5 appears to the OS as a single large volume. The objectives with RAID 10 are twofold: independent and simultaneous accesses to multiple drives and fault tolerance. It is a stripe of multiple independent mirrors.The basic text diagram gets mangled in a post. See the diagrams in this link.
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Our new server uses basically that kind of scheme with the OS being mirrored and the data being on a separate RAID 5. Now, I'm wondering if I should bite the bullet and reconfigure the data drives. Unfortunately, I don't have the luxury of 8 drives. I've got 4 300GB drives and need to decide what the optimal use would be. Obviously, security is number one as we've only using 100GB or so now and likely won't need more than another 150GB or growth over the life of the server.
-Rod
My eight drive comment relates to the equivalent requirement of your current five drive array on the older server. Regardless of the number of drives used in a RAID 5 array, one's capacity is "lost" to provide the check bit. With 5 drives, you get the capacity of four. To maintain that capacity in a RAID 10 array, that number would be doubled.Having read your latest response to Abe, however, the new array has larger drives where you don't need all that capacity. You could afford to mirror everything which is what RAID 10 is all about. Using four 300 GB drives, that would provide 600 GB in a RAID 10 configuration and 900 GB in RAID 5.
Sounds like you could splurge and get a more robust array using 10.
Let me also take a moment to thank you for making this incredible nut house possible!
Thanks, and thanks for the advice. Unfortunately, Dell doesn't support a real RAID 10. Basically, you get 1 or 5. Though 1 shows a stripe, so I'm not sure how it really works. LSI controller with Dell front end.I went ahead and a testing it as a RAID 5 with hot swap and pulled a drive, hot no less. It now shows the hot swap as rebuilding and the reinserted drive as ready. Hmmm. Once it rebuilds the hot swap, I wonder if ready will become the new hot swap. Of course, I won't find out until tomorrow morning.....and the logical is empty!
-Rod
at least two of my customers have Dell boxes using RAID 10. Strictly speaking, what I'm referring to is RAID 1+0. Admittedly, one system was originally configured as 0+1 and I had to explain to the guy the difference, but it is simply running multiple separate drives that are mirrored.
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