Nomenclature: SSD is a physical device that plugs into an electrical disk slot. Flash is a PCIe card. Both use the same underlying back end storage technology (flash chips of SLC, MLC, and related).
I’ve had a while to do some testing with a large number of SSD units in a single device. I can give you a definite sense of what I’ve been observing.
First: SSDs are, of course, fast for certain operations.
Second: there’s a whole lotta er … marketing numerology … around SSDs.
Ok. So imagine we have 48x very late model Sandforce 22xx equipped SSDs, in a single chassis. Call this thing an SSD array. Imagine that we’ve done some experimentation on various RAID cards. Including some from a vendor that has not been announced/released. Including some dumber HBAs.
If we believe the underlying theory behind SSDs, and aggregates of the same, for reasonable configurations of SSD (that does not mean RAID0s, but RAID5’s with a smaller chunk size), we should be able to approach the theoretical maximum number of IOPs, assuming that the RAID calculation engine can keep up with the SSD.
This assumption is, sadly, incorrect.
Theoretical maximum IOP rate for this unit, assuming the vendors don’t … er … embellish too badly … is about 2.4M IOPs. After putting them into RAID5’s best possible case should be 2.1M IOPs.
What do we achieve?
Color me unimpressed. You have a “disk” drive, you expect all the trappings of that “disk” drive to work. Like activity lights. So you plug this device into a backplane that lights its activity lights from the disk. And it doesn’t work. Speaking with the backplane folks, they get their signals from the disk. Speaking … Read moreInteresting comment from an SSD vendor support person