i was looking up in the sky just now and wondering if anyone here would know how many HDD's in raid it would take to meet the speed of a single standard run of the mill SSD these days lol
google ~ raid vs ssd
It's highly dependant on what SSD and what HDD we're comparing.
a regular SATAIII SSD with not too many bells and whistles should hit 500MB/s Read
NVME and M.2 ssds will easily go beyond 1.5GB/s
a hdd should hit around 100MB/s Read. More it's a performance drive (WD Blacks can hit 175+?), Less if it has some age. (performance is also better at the beginning of platter)
4 or 5 times faster typically...
Now if we're talking 4K randoms the SSD will run even more circles around HDDs
a typical SSD will hit probably 20-25MB/s 4k Random Reads while a HDD will be stuck under .5-1MB/s
This is because the R/W head on a physical drives needs to move physically to find the right place. SSDs have no parts. in that case easily 30x more performance
Here's are community some benches
https://forum.teksyndicate.com/t/storage-benchmark-thread/73753
As for your question...
Depends on the drive and what metric your looking to match.
Either way with raid and any form a parody/striping you're going to hit and upper limit when diminishing returns kicks in after 3 or so drives
If you were stupid enough you could match a Sata 3 ssd in read and write speeds by Raiding 4, maybe 3 (if they are higher rpm drives), in a raid 0. They would have to be something like a WD black, or a similar performing drive. They would match a sata 3 ssd in read and writes, but other stuff like 4k iops, they would get destroyed. It is neither an economical or reliable solution. If you want to compare to something like a Samsung sm951 or Intel 750 series ssd, your going to need 20+ drives in a raid 0 which is a ridiculously laughable thought.
There are the Seagate Cheetah drives. They spin up to 15000 rpm but only have sub 1 TB capacity. They would give a SSD in some applications a run for it's money. They go up to 200 Mb/s.
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the 7200 seagate drives have sequential reads of 170-180 MB/s. That said the most noticeable fact about an SSD is the access time and with HDD raid that only gets worse :D as then it's as fast as the slowest lookup of the drive in the raid setup for every action.
I think @NJM1112 said it best. Getting HDD to match the speeds of an SSD is a pipe dream. But if money was no object just spend about 12k on the fastest drives possible in raid 0 and then for the first 10 minutes it might be as fast as a 200$ SSD.