I recently made a RAID5 from a pack of a brand new WD10JUCT (1Tb, 5400, 512e, 3Gb/s!, but! CMR) and under Windows softraid they showed up to 500MBs of sequential reads/writes. Sure, when I installed them in R720 with PERC which doesn't understand 512e/4kn drives and then slapped VMDKs on it... things got slow but not 25-30MB/s.
And my experience with different RAIDs says RPM doesn't really matters, you would get N x Usable_Stripe_Count MB/s in sequential access anyway and with enough spindles you would get fine enough access time too.
Probably there was a problem somewhre else, like 30MBs is clearly up to USB2 speeds and even 4200rpm should show a better numbers.
That particular build worked fine, it was just really slow. It was a very ill-advised plan to begin with - I was using 5.25" -> 2.5" hotswap bay converters for the 2.5" laptop drives. The idea at the time I guess was less noise and power, but mostly it was just to say I did it I think.
Other than it being extremely slow it lasted as my home NAS for 5 or 6 years until I outgrew it.
These days I run a 250TB ZFS pool as my "main" pool, utilizing the 8TB Seagate SMR drives of yesteryear. I have had very little problems with them, but it was a very careful pool design after many years of running ZFS on production systems. So far I've had a few drive failures (as expected) and we are probably ticking closer to decade than I'd like to admit. It performs far better than I need it to - as it's very much WORM style storage for backups and media.
I recently made a RAID5 from a pack of a brand new WD10JUCT (1Tb, 5400, 512e, 3Gb/s!, but! CMR) and under Windows softraid they showed up to 500MBs of sequential reads/writes. Sure, when I installed them in R720 with PERC which doesn't understand 512e/4kn drives and then slapped VMDKs on it... things got slow but not 25-30MB/s.
And my experience with different RAIDs says RPM doesn't really matters, you would get N x Usable_Stripe_Count MB/s in sequential access anyway and with enough spindles you would get fine enough access time too.
Probably there was a problem somewhre else, like 30MBs is clearly up to USB2 speeds and even 4200rpm should show a better numbers.