The ExaDrive NL is being presented as a better value option of the company’s existing TLC flash ExaDrive DC, which can pack in 100TB but won’t leave much change out of £30,000 per drive. And all this in a flash drive market in which large capacity would usually be something in the 7TB to 15TB range.
The ExaDrive NL is available with SATA and serial-attached SCSI (SAS) connectivity, with the idea that these drives are a high-capacity, low power-consumption replacement for spinning disk drives that currently run to about 18TB capacity-wise. Additionally, solid-state drives (SSDs) such as these are not subject to failure of read/write heads that can come with the movement and vibration that affects hard disk drives (HDDs).
“The ExaDrive NL costs three or four times the price of a classic hard drive per GB,” said Marc Staimer, analyst at Dragon Slayer Consulting in the US. “But this is offset by the savings in electricity, cooling and space that it can bring in the datacentre.”
Use cases Nimbus has in mind for these SSDs include media streaming, use in analytics data lakes, and for archiving.
The key point is that in all these use cases this type of flash storage – ie, QLC flash – is not subject to intensive input/output (I/O). Nimbus’s ExaDrive products are not aimed at access patterns characterised by lots of random I/O, which SSDs usually target, and the new NL unit is even less so than its TLC predecessor.
ExaDrive DC and NL drives can attain read throughput of 500MBps and 114,000 IOPS and 460MBps and 105,000 IOPS on writes. That’s way better than the 150MBps/1,500 IOPS of a SAS HDD or the 60MBps/900 IOPS of a SATA hard drive.
However, that’s inferior to the 4.4GBps and 489,000 read performance and 3.2GBps and 222,000 IOPS of the Kioxia (formerly Toshiba Memory) with its new generation 24G SAS connectivity.
ExaDrive units obviously also perform less well than non-volatile memory express (NVMe) SSDs, given their SAS/SATA connectivity. The NVMe Intel D7-5000, for example, claims 7GBps throughput and 1 million read IOPS with 4.3GBps and 130,000 input/output operations per second (IOPS) during writes.
The new Exadrive NL is presented as a more economic option because it is built from cheaper NAND QLC components, while the ExaDrive DC is based on TLC components that wear out much less quickly.
On a price/capacity basis ExaDrive DC is $400 per TB in a drive that’s guaranteed for five years without regard to the number of writes per day. Meanwhile, the ExaDrive NL claims $170 per TB for a five-year drive life, provided writes don’t exceed 20% of the platter surface a day.
The lifetime – as affected by the loss of conductivity in NAND cells under assault from electric charge – is the Achilles heel of flash drives. MLC drives support three levels of charge to provide four states with two bits of information per cell. Meanwhile, QLC cells support 16 levels of voltage, which corresponds to four bits per cell. So, QLC offers double the capacity of MLC, but ages twice as quickly too.
“Initially enterprises thought QLC SSDs wouldn’t be durable enough for serious use in servers and storage arrays, despite their lower cost compared to MLC and TLC flash,” said Jim Hardy, a semi-conductor specialist at analyst Objective Analysis.
Nimbus isn’t the only flash supplier to offer high capacity SSD. Pure Storage has 49TB QLC DirectFlash drives for its FlashArray//C. In February, IBM announced the 38.4TB FlashCore Module for its StorWize arrays, also based on QLC flash, Capacities are lower than the Nimbus drives but not the speeds.
The Pure and IBM drives are NVMe-connected, and targeted to equip SAN arrays. Nimbus’s ExaDrive, on the other hand, are aimed at all makes and types of server or disk array. Dell EMC, HPE, Lenovo, Cisco and SuperMicro have already validated them.
The bigger capacity of the Nimbus drives is down to their format, being 3.5” compared to the 2.5” of most other enterprise SSDs. Inside, there are four NAND cards and a controller card. That much electronics crammed into such a space requires a number of cooling holes, but still less heat is released than in a spinning disk HDD, with wattage between 10w and 14w.
Exadrive NL will also be available in smaller capacities – 32TB and 16TB.