We’ve done this exercise recently for multi-petabyte enterprise storage systems.
Not going to name brands, but in both cases this is usable (after RAID and hot spares) capacity, in a high-availability (multi-controller / cluster) system, including vendor support and power/cooling costs, but (because we run our own datacenter) not counting a $/RU cost as a company in a colo would be paying:
HDD: ~60TiB/RU, ~150W/RU, ~USD$ 30-35/TB/year
Flash: ~250TiB/RU, ~500W/RU, ~USD$ 45-50/TB/year
Note that the total power consumption for ~3.5PB of HDD vs ~5PB of flash is within spitting distance, but the flash system occupies a third of the total rack space doing it.
As this is comparing to QLC flash, the overall system performance (measured in Gbps/TB) is also quite similar, although - despite the QLC - the flash does still have a latency advantage (moreso on reads than writes).
So yeah, no. At <1.5× the per-TB cost for a usable system - the cost of one HDD vs one SSD is quite immaterial here - and at >4× the TB-per-RU density, you’d have to have a really good reason to keep buying HDDs. If lowest-possible-price is that reason, then sure.
Reliability is probably higher too, with >300 HDDs to build that system you’re going to expect a few failures.
We’ve done this exercise recently for multi-petabyte enterprise storage systems.
Not going to name brands, but in both cases this is usable (after RAID and hot spares) capacity, in a high-availability (multi-controller / cluster) system, including vendor support and power/cooling costs, but (because we run our own datacenter) not counting a $/RU cost as a company in a colo would be paying:
Note that the total power consumption for ~3.5PB of HDD vs ~5PB of flash is within spitting distance, but the flash system occupies a third of the total rack space doing it.
As this is comparing to QLC flash, the overall system performance (measured in Gbps/TB) is also quite similar, although - despite the QLC - the flash does still have a latency advantage (moreso on reads than writes).
So yeah, no. At <1.5× the per-TB cost for a usable system - the cost of one HDD vs one SSD is quite immaterial here - and at >4× the TB-per-RU density, you’d have to have a really good reason to keep buying HDDs. If lowest-possible-price is that reason, then sure.
Reliability is probably higher too, with >300 HDDs to build that system you’re going to expect a few failures.