OCZ’s latest Z-Drive R4 series PCIe SSD

OCZ just released a new version of their enterprise class Z-drive SSD storage with pretty impressive performance numbers (up to 500K IOPS [probably read] with 2.8GB/sec read data transfer).

Bootability

These new drives are bootable SCSI devices and connect directly to a server’s PCIe bus. They come in half height and full height card form factors and support 800GB to 3.2TB (full height) or 300GB to 1.2TB (half height) raw storage capacities.

OCZ also offers their Velo PCIe SSD series which are not bootable and as such, require an IO driver for each operating system. However, the Z-drive has more intelligence which provides a SCSI device and as such, can be used anywhere.

Naturally this comes at the price of additional hardware and overhead.   All of which could impact performance but given their specified IO rates, it doesn’t seem to be a problem.

Unclear how many other PCIe SSDs exist today that offer bootability but it certainly puts these drives in a different class than previous generation PCIe SSD such as available from FusionIO and other vendors that require IO drivers.

MLC NAND

One concern with new Z-drives might be their use of MLC NAND technology.  Although OCZ’s press release said the new drives would be available in either SLC or MLC configurations, current Z-drive spec sheets only indicate MLC availability.

As  discussed previously (see eMLC & eSLC and STEC’s MLC posts), MLC supports less write endurance (program-erase and write cycles) than SLC NAND cells.  Normally the difference is on the order of 10X less before NAND cell erase/write failure.

I also noticed there was no write endurance specification on their spec sheet for the new Z-drives.  Possibly,  at these capacities it may not matter but, in our view, a write endurance specification should be supplied for any SSD drive, and especially for enterprise class ones.

Z-drive series

OCZ offers two versions of their Z-drive the R and C series, both of which offer the same capacities and high performance but as far as I could tell the R series appears to be have more enterprise class availability and functionality. Specifically, this drive has power fail protection for the writes (capacitance power backup) as well as better SMART support (with “enterprise attributes”). These both seem to be missing from their C Series drives.

We hope the enterprise attribute SMART provides write endurance monitoring and reporting.  But there is no apparent definition of these attributes that were easily findable.

Also the R series power backup, called DataWrite Assurance Technology would be a necessary component for any enterprise disk device.  This essentially saves data written to the device but not to the NAND just yet from disappearing during a power outage/failure.

Given the above, we would certainly opt for the R series drive in any enterprise configuration.

Storage system using Z-drives

Just consider what one can do with a gaggle of Z-drives in a standard storage system.  For example, with 5 Z-drives in a server, it could potentially support 2.5M IOPs/sec and 14GB/sec of data transfer with some resulting loss of performance due to front-end emulation.  Moreover, at 3.2TB per drive, even in a RAID5 4+1 configuration the storage system would support 12.8TB of user capacity. One could conceivably do away with any DRAM cache in such a system and still provide excellent performance.

What the cost for such a system would be is another question. But with MLC NAND it shouldn’t be too obscene.

On the other hand serviceability might be a concern as it would be difficult to swap out a failed drive (bad SSD/PCIe card) while continuing IO operations. This could be done with some special hardware but it’s typically not present in standard, off the shelf servers.

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All in all a very interesting announcement from OCZ.  The likelihood that a single server will need this sort of IO performance from a lone drive is not that high (except maybe for massive website front ends) but putting a bunch of these in a storage box is another matter.  Such a configuration would make one screaming storage system with minimal hardware changes and only a modest amount of software development.

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