Just wondering... external Raid enclosures for SSD's?

L

Lumpus

Limp Gawd
Joined
Sep 2, 2005
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Seeing a few threads lately about various cheap 500/1000gb SSD's, I was wondering if any vendor had created an external Raid enclosure for stacking 6-10 SSD's together in a single virtual array? That (eventually) might be a way to retire an older (but big) HDD... or would the external link lose some/all of the SSD's innate speed advantages?
/just an idle thought...
//can't brain today :/
 
So, most hardware RAID adapters have onboard CPUs that can handle a certain amount of throughput. This isn't much of a limiting factor with spinning disks, but when you've got an array of 8 SSDs instead of 8 HDDs then you can quite quickly saturate the capabilities of the CPU on the RAID controller. In that way, you might 'lose' out on a bit of the combined SSD speed because the controller's CPU holds you back. On the other hand, that only happens because you're going so fast the controller can't keep up so unless you're big enterprise and need stupid amounts of speed, it's hard to think of that as much of a limitation.
 
Also consider your connectivity throughput, 20000/mbps sounds great, but limiting on a 640/mbps usb 3.0 port.
 
BoiseTech has a good point; a single SATA SSD can more-or-less saturate a USB 3.0 Gen 1 connection (USB 3.0 Gen 1 is 5 Gbps, SATA3 is 6 Gbps and SATA SSDs commonly saturate a SATA3 connection).

Of course, you could go with something like external SAS which has higher bandwidth, with connections as high as 48 Gbps. At that point though things will be expensive.

With all that said, keep in mind that for most folks the thing that makes SSDs 'feel' fast isn't their transfer rate, it's their super low latency. For lots of folks the difference between a SATA SSD (running at ~550 MB/s) and a NVME SSD (running at ~2000 MB/s) is difficult to feel, because the latency numbers are already so small. So targeting faster transfer rates may not actually yield tangible benefits, unless you've got a specific use case where it applies.
 
I second the point above about the latency being more important then the seq transfer rate.

That said it is not impossible. USB 3 in whatever form is impractical because USB is a polling based bus and will add latency (and lots of it). The added USB latency will be most visible in the small random IO which your OS loves to do.

If you really want all the speed you can get, go for 12GBit SAS connection and external enclosure. The broadcom SAS controllers are good at keeping latency under control.

Or if you want to go really nucking futs, use an AMD Epyc based system and connect your 8 SSD's via x4 NVME. Then you can have the fastest game loading times ever, combined with crap framerates because the Epyc's are really not gaming cpu's :)
 
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