Yes, I believe either your controller or the raid backplane is bad. But I think the controller is the culprit. Can you look up the firmware version of the RAID controller (not to be confused with the system BIOS, which you should also check) and compare to what is available on Dell's site? You may find the version is quite old and that critical issues have been resolved in newer versions. Alternatively you could try calling Dell support - which you should certainly do if support is available! You can easily check what service contract is in force by looking up the Service Tag at support.dell.com.
Two notes of caution. You are in dangerous territory. Upgrading the RAID controller firmware can sometimes result in data loss - make sure the new version has been out for awhile, and read the release notes carefully. 2) RAID 5 doesn't give you a lot of wiggle room. Either way prepare to back up your critical data before you let time pass on this issue or take any substantial corrective actions!
It's not possible to say precisely what the odds of X drives going out in Y amount of time are, but it is safe to say that drive failures are not completely independent, as commonly assumed. Multiple disk failures in the same array within close temporal proximity are actually a fairly common occurrence.
Less than a month ago, we had 4 drives fail over the same weekend on one of our production servers (same RAID set), one after another. Almost as soon as we replaced one drive, another failed... we ultimately ended up replacing all 7 drives, to be safe.
One reason, as you mentioned, is that the rebuild process is disk-intensive, so there's a non-trivial chance that a disk teetering on the edge of going bad will be pushed over the edge and fail, as a result of the increased stress it's under in providing data to rebuild the new disk.
Another factor to consider is that all the members in a RAID array tend to be in the same physical environment, and subject to very similar physical stresses (heat, vibration, power fluctuations, etc.), which tends to result in a higher incidence of similar failure times than you'd see with disks in different environments.
And, if you're like most people, you probably just bought 4 identical disks from the same place, and ended up with 4 disks from the same batch, resulting in the 4 disks sharing identical manufacturing characteristics (any defects or anomalies during that manufacturing batch are likely shared across all four disks). So identical disks in an identical environment... makes sense that they might share other similar characteristics, such as when they fail.
Finally, there's the fact that disk failures are not normally distributed (as in a bell curve). They tend to have higher failure rates at the beginning of their lives (infant mortality), and after a long period of time, when they wear out and die due to the physical stresses they've been subjected to, with a relatively lower rate of failure int he middle (the bathtub curve).
So, yes, multiple drive failures in the same RAID array happen with some regularity, and is one of the reasons you always want good backups.
Best Answer
This error corresponds to the cache module on the controller. At this point, you need to probably replace the RAM or the actual PERC controller. This should be standard warranty work.