Zstor flash JBOF shows the limits of NVMe/NVMf

German storage supplier Zstor has uprated the JBOD (Just a bunch of disks) for the NVMe flash era and produced the JBOF.

The NV24P allows for up to 24 2.5” NVMe-mounted flash drives of up to 8TB for a total capacity of 184TB.

Connectivity is to up to eight servers and is via what appears to be NVMe over fabrics (NVMf), in this case RDMA (Remote Direct Memory Access), with NVMe drives aggregated using PCIe switching.

So, what the Zstor JBOF provides is direct-attached storage (DAS) for hosts with none of the functionality expected of a shared storage array.

Without giving any exact figures Zstor promises access times similar to those for server-located flash, which must mean in the low hundreds or tens of milliseconds.

The Zstor NV24P illustrates the current limits of NVMe, a PCI-based standard that potentially allows flash storage to break through the limits imposed by SCSI and its use in the disk-era SAS and SATA protocols.

In other words, NVMe is a direct slot-in for PCIe flash in the server with no performance hit. With NVMf, using for example RDMA – a direct connection as if memory – as here, it can also provide near server SSD performance.

But it cannot provide storage addressing and provisioning, RAID, features such as data protection, data reduction etc that have been traditionally provided by a controller.

And so this is effectively a DAS solution, albeit one with uses because to add a controller would lop off the benefits in performance that NVMe brings as it carries out the processing needed to do them.

This controller bottleneck is an obstacle in the road to fulfilling the potential of NVMe in a true shared storage array format.

We await the vendor that can build in the functionality brought by a controller but with the power to overcome any hit to performance.