Hi William,
SOmething to think about. Let's suppose a channel/cable completely dies. How would you protect against it? Split a logical mirror device over 2 channels.
This effectively implements RAID 0+1, right? RAID 1 (mirroring) over RAID 0 striped volumes. I can certainly see your point regarding the redundancy of the controller channels, but my understanding is that (apart from that) RAID 0+1 is less robust that RAID 10 regarding disk failures. Presuming that the system will continue to operate even in the event of 1 channel failure, it's still not a clear choice. Does that seem like a reasonable assessment?
I'm not sure why people say one is better than the other. Both will survive the loss of 2 drives -- they're just different drives.
RAID 0+1: A(1m1) s B(1m1) <-- any drive on A and any drive on B RAID 10: A(1s1) m B(1s1) <-- both drives on A or both drives on B
Either way, I think you can do both across 2 channels to be redundant for a channel/cable failing.
RAID 0+1: C1-m-C2 s C1-m-C2 RAID 10: C1-s-C1 m C2-s-C2
Another trick I've started doing with my MegaRAID setups is mirroring in hardware but striping in software.
Yeah, that is a good point. I havn't decided either way but I consider that a viable option.
You can probably do the same hardware + software trick for RAID10. Except after OS crashes, Linux+Solaris spends quite a bit of time resyncing mirrors and it looks like the MegaRAID controller is a bit smarter in knowing when to resync.
If you were building this system now, and want the option of buying the same disks in 3 years time, do you think it would be a bad idea to go for the ~40GB size? Maybe the next size up would be better, though we don't actually need the extra space.
Always get more space than you need if you can afford it because it's a pain in the ass adding more disk space. Especially on the boot drives.
Also, someone asked me what happens if one of the CPUs fails on this system, will the system continue to operate on 1 CPU. I havn't really considered this, and have never read anything either way, so my assumption is "no, it won't". Any comment?
Doing a google search for "hot swap cpu", I see they've added something into Linux but you'd still need hardware support.
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