Is it slower to write one block in RAID Level 5 with 5 disks than RAID 1 with two disks (mirroring only)? I think No since with Level 5 you are writing the data and the parity (two writes). With Level 1, you are writing twice as well (original as well as mirror). Can someone let me know if my train of thought is correct?
In RAID-5, unless your write was large enough to cover all data chunks for a given parity chunk, it has to read the missing data chunks in order to be able to recalculate and update parity. Thus a relatively small write on a RAID-5 can turn into a large read operation.
RAID-1 does not need such additional reads, as there is no parity, it just writes to all disks directly. So it's possible that RAID-1 (or RAID-10) is faster for random small writes.
Even so it's hard to tell what's faster or slower overall. It's best if you benchmark it yourself directly for your specific use case scenario.