New Dell PE R710 – Storage

1. No, the PERC H700 Adapter will not be a bottleneck for 16 spinning rust disks.
2. You want the members of each RAID-1 pair on different channels and expanders, in order to increase reliabiity. That way a bad cable, channel, or expander doesn't take the whole RAID-1 set offline. A 15K spinning rust disk can only do about 2 Gbps max with sequential reads, so you can put three disks these per 6 Gbps channel. Often you can do much more than threee, because only backups really do streaming sequential reads or writes. All real workloads have a lot of random IO, which will bring even a 15k disk down to just a few MB per second in throughput.
3. Yes, you can mix disks, but why? Also, why aren't you using RAID-10 instead of a bunch of separate RAID-1 arrays?
4. Unfortunately no, but any standards-compliant SAS Expander will work.

The real suggestion I would make is this: Unless you are running the large hadron colider, in general aggregate disk bandwidth doesn't matter, only IOPS matter for the overwhelming majority of workloads. Stop trying to make spining rust disks fast - they aren't. Disk is the new tape.

If you need performance, most workloads need IOPS more than bandwidth or capacity. Buy your Dell server with the cheapest SATA drives (to get the carriers), and then replace those cheap SATA drives with smallest numbber of Intel 500-series SSDs that meets your capacity needs. Dell's SSD offerings are terribly overpriced comparted with Intel SSDs from say NewEgg, even though the Intels perform better and are more reliable than whatever Dell is shipping for SSDs (Samsung?).

Make one big RAID-5 array of SSDs. Even just 3 modern MLC SSDs in RAID-5 will absolutely destroy 16 15k spinning rust disks in terms of IOPS, by a factor of 10x or more. Sequential throughput is a non-issue for most applications, but the SSDs will also be 2x faster than spinning disks in that regard. Use large capacity 7.2k SATA disks for backup media or for archiving cold data. You'll spend less money and use less power with SSDs.

Resistance to SSDs over reliability are largely FUD from conservative storage admins and SAN vendors who love their wasteful million-dollar EMC arrays. Recent "enterprise MLC SSDs" are at least as reliable as mechanical disks, and probably much more reliable (time will tell). Wear leveling makes write lifetime a non-issue, even in the server space. Your biggest worry is firmware bugs rather than hardware failure, which is why I suggest going with Intel SSDs.

RAID 1 is a mirror. The fact that when you drill down into the virtual disk, you only see Physical Disk 0:0 means that Disk 0:1 has failed and is showing as removed.

You could try removing the faulty disk (should be showing with an orange light) and re-inserting it - this sometimes kicks off a rebuild but even if that works you should probably consider replacing the drive to be on the safe side.

If the drive needs replacing, check if you have pro support on that server before you go buying anything - Dell will send you a new one for free if you have, but they'll probably ask you to do a DSET report first.

It's unusual for the Dell OMSA console to show a RAID virtual disk as degraded but the physical disks as not having any problems. Try refreshing the physical disk status to see if anything changes.

EDIT: From the hardware log you posted, it does look like disk 0:1 failed and then came back online. Normally, if OMSA thinks the hardware looks OK, this would let you initiate a rebuild of the array. You might want to try this but I would expect the disk to fail again before long.