1) Is the difference in physical disk sizes causing the issue?
>> I don't think so, but is the drives all detects and there is no errors? Are the new drives have the same specifications other than size?
2) Will I be able to perform the operation in the Disk console if I reboot?
>> Disk console, by mean the PERC BIOS Utility? Yes, the operation is done at the PERC BIOS or OMSA (OpenManage Server Admin). But before you do anything, please do a full data backup
3) Can I mix in disks from another vendor into this virtual disk (have some spare 600GB Lenovo disk)
>> You can, as long as they are detected and when you do the expansion, it can be selected. But I can't guarantee that it will work flawlessly without any errors as PERC, BIOS, Disk backplane communicates with Dell disk firmware.
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