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Hitachi Vantara recently introduced new versions of its Hitachi Virtual Storage Platform (VSP) models VSP E590 and VSP E790 for small and midsized enterprise clients. New hybrid storage options give clients the flexibility to consolidate diverse workloads in a single midrange platform. Initially launched as NVMe-only platforms, the VSP E series portfolio was targeted specifically at applications that required ultra-low latency and persistent high performance. The latest expansion of the VSP E series portfolio includes the addition of new media options for VSP E590 and VSP E790. These options give users the flexibility to meet the requirements of varying workloads with the ability to intermix NVMe SSD, SAS SSD (solid state drives) and SAS HDD (hard disk drives). They help ensure that clients never compromise performance while making use of high capacity, low-cost media for data retention. Featuring a simple, self-install setup with embedded management, VSP E series systems can be up and running in 30 minutes.
IDC predicts that hybrid flash and HDDs will continue to be a significant market through 2025, as shown in the chart below.*
While NVMe SSDs provide the highest performance, they are more costly than 10K HDDs and nearline 7.6K HDDs, and not all applications need the higher performance of SSDs, much less NVMe SSDs. The cost-effectiveness of HDD storage makes it a good fit for backup, archiving, disaster recovery, Tier 2 applications and test/dev use cases. The difference between NVMe SSDs and SAS SSDs is not so much a matter of cost but available connectivity.
NVMe connects directly to the PCIe bus on the controller’s computer and does not have the overhead associated with an SAS connection, which is in place to support SCSI devices like HDDs. All that overhead is stripped out, so latency is much lower. NVMe was designed to support 65,000 queues, each having a queue depth of 65,000 while SAS supports one queue with a 256-queue depth. On the other hand, since the NVMe device connects directly to the PCIe bus, it is limited to direct attach, while SAS devices can connect outside of the controller to hundreds of devices.
VSP E590 and VSP E790 are packaged in a 2U drawer, which contains dual controllers, dual power supplies and batteries, 24 external connections, and 24 internal 2.5-inch NVMe SSDs. With 30TB SSDs, that is a total of 720TB of raw storage capacity all in a 2U drawer, the ideal package for small and midrange high-performance storage requirements. However, not all applications need that level of performance all the time.
One capability that the VSP E series did not offer until now was the support of hybrid storage, SSDs and HDDs. Other NVMe midrange systems, like Dell/EMC, Pure, NetApp, and HPE do not support hybrid storage: It is hard to cram that support into a 2U form factor controller that is already crammed full of the functions and features to support NVMe SSD storage. To support hybrid storage, you need redundant SAS adapters and connectors, and software for SCSI access and management of HDDs.
Hybrid support is now available in the VSP E590 and VSP E790 with the addition of expansion drawers that contain SAS SSDs as well as SAS HDDs. The expansion drawers are connected to the base controller drawer through the external ports with SAS cables. The software was already there since it is in the same Hitachi Storage Virtualization Operating System RF (SVOS RF) that is common to all VSP systems. There are a number of different configurations to satisfy every requirement, as shown in the table below.
The base 2U chassis can contain 24 internal NVMe SSDs, which be as large as 30TB. The small form factor 2U expansion drawer can contain 24 x 2.5-inch drive modules, which can be SAS SSDs or 10K SAS HDDs. (10K refers to the RPM speed of the HDD.) The large form factor expansion drawer is also a 2U drawer that contains 12 x 3.5-inch nearline SAS HDDs, which are mounted horizontally in the drawer. The NL-SAS HDDs rotate at 7.5 RPM and are a cost-effective storage for backup, archiving, disaster recovery, Tier-2 applications, and test/dev use cases. The dense form factor drawer is 4U and contains 60 x 3.5 NL-SAS or 10K SAS HDDs, which are mounted vertically and accessed from the top of the drawer for the most cost-effective storage option. A VSP E590 or VSP E790 can have up to 10 expansion drawers for a maximum of 552 drive or 8.9PB of raw capacity!
With that much capacity, the next upgrade can be very disruptive without a new migration feature, which we call data-in-place (DIP) migration. The enterprise VSP 5000 series comes with a DIP, nondisruptive upgrade path from the current generation to the next generation of technology, the VSP 5200 and VSP 5600. Since the VSP 5000 starts with two nodes with two controllers in each node, the controllers can be replaced, one at a time, until all of them are replaced and the upgrade is complete. The swap out of a controller takes 25 or 50 minutes for a node. In a six-node system, this would take 300 minutes or 5 hours plus 3 hours for additional tasks. All this occurs while the data continues to be accessed off the same drives. No data migration is required, and the multiple controllers ensure that there is no single point of failure during the controller replacements.
DIP is more difficult to do in the VSP E series, which only has two controllers. With dual controllers, one controller would have to be offline, creating a single point of failure. Hitachi Vantara solves the single-point-of-failure exposure by connecting the next-generation VSP E series to the same set of expander drawers that are connected to the previous-generation VSP E series. We then transfer the controller functions across a high-speed interconnect between the two VSP E series base units. This requires connections to the expansion drawers from the new-generation controllers, and communication between the new and old controllers.
While the new VSP E series controllers are not available today, we can prepare for DIP by installing the connections as we add the expansion drawers. In the table above there are two types of small form factor expansion drawers: the DBSE and the DBS2. The DBS2 has additional SAS ports for connection to the next-generation controllers. If you don’t see the need to plan for a DIP replacement, then you can get the DBSE, which does not have the additional SAS ports. The DBS2 must be the first drawer in the string connected to both controllers as shown below:
In addition to reserving two SAS ports on the DBS2 for future connection to the next-generation controllers, we need to reserve two sets of high-speed interconnect ports for connection between the current VSP E series controllers and the next-generation VSP E series controllers.
If you plan to install a hybrid VSP E590 or hybrid VSP E790 and plan for DIP migration to the next-generation VSP E series system, you will need to configure the slot A I/O boards for Fibre Channel or iSCSI external connections. Then, configure the slot B I/O boards for the SAS connections, and the slot C I/O boards for high-speed interconnect to the next-generation VSP E series controllers when they become available.
For more information on the new VSP E590 and VSP E790 midrange storage systems read the VSP E series datasheet on hitachivantara.com.
Hu Yoshida is CTO Emeritus at Hitachi Vantara.
