EMC crashes the server flash party

Limitations and futures

VFCache has to be disabled and removed for vMotion to take place, it being a local resource for the virtual machine. It's not possible to configure automatic ESX server failover if it's being used and things like vCenter Site Recovery Manager with it or use it in a cluster that uses vMotion to balance workloads.

The VFCache card can have separated off DAS partitions for server app use but data loaded into them is not written to the back-end array. This is called split-card mode. It should only be used for temporary data, stuff that doesn't need safeguarding by being written to the back-end array

EMC will add deduplication to VFCache later this year, increasing its effective capacity. It does not say where the deduplication will be done, with our assumption being that it will be less burdensome on the host CPU to have it carried out on the card itself.

There will be additional capacity points in the future and VFCache will be more deeply integrated with EMC's storage management products and with the FAST architecture. This could be a hint that EMC's storage arrays will co-ordinate more actively with VFCache.

VFCache and Fusion-io

Fusion-io has sold to early adopters in EMC's view. It believes Fusion-io-type server DAS approaches do not protect data against a server crash or provide data sharing. By storing the server's data in a back-end array it scan be protected via snapshots, replication, etc, and made available to other servers. Management is also easier. Mainstream server flash use won't happen unless these data protection and management features are added.

Specifically, MC says VFCache is less of a drain on server resources than a Fusion-io flash store because because VFCache hands off flash and wear-level management to the PCIe card itself, whereas the host CPU does this for the Fusion-io product. It says Fusion-io CPU overhead could be up to 20 per cent higher than that with VFCache.

Development and Project Thunder

EMC will add deduplication technology to VFCache later this year, enabling an effective increase in capacity. Clearly this will best be carried out on the card to avoid burdening the host CPU. Whether that will be the case remains to be seen.

There will be larger capacity points for VFCache, possibly going beyond 300GB, and different form factors, adding blade environments to the current rack form factor. It will also integrate better with EMC storage management technologies, and there will be additional integration with FAST architecture. This means active co-ordination between caching by VFCache and EMC's VMAX and VNX array FAST capabilities. We'll be seeing:

- Enhanced VMAX/VNX array integration – hinting, tagging, pre-fetch for even greater performance
- Distributed cache coherency for active-active clustered environments
- VMAX and VNX management integration

EMC has also announced Project Thunder, a "low-latency, server networked flash appliance that is scalable, serviceable, and shareable. It is intended to "deliver I/Os measured in millions and timed in microseconds."

This suggests it will use a fast server-appliance interconnect such as InfiniBand, which Oracle uses in its Exadata systems, or some form of PCIe I/O virtualisation. EMC confirmed this and said it will be working with its customers in a second quarter early access program to determine the interconnect to use.

It will be "optimised for high-frequency, low-latency read/write workloads" and will build upon the PCIe technology in VFCache. In effect this will provide a combination of the functionality offered by Fusion-io and Violin Memory products; the speed of directly-attached flash and the sharability of a networked flash memory array.

El Reg thinks other mainstream storage, PCIe flash storage, server/storage and flash array vendors will be forced to follow suit, giving a boost to either InfiniBand or IOV high-speed server-storage interconnect technologies, or both.

Storage flash landscape

VFCache is a fast fix to the threat - and opportunity - posed by Fusion-io and other PCIe flash caching suppliers to EMC on the one hand, and networked flash arrays such as those from Violin Memory, WhipTail and Nimbus now, and startups like Pure Storage, SolidFire and XtremIO on the other.

As with the introduction of SSDs into storage arrays, EMC is the first mainstream vendor to jump on the server PCIe flash bandwagon. We understand Dell is actively working in this area and expect HP, IBM and NetApp to follow suit together with Fujitsu and, maybe, HDS. It represents a recognition that disk drive latency is no longer acceptable for primary data access and that network latency is also becoming unacceptable.

Virtualised, multi-socket, multi-core, multi-threaded servers demand faster I/O than Ethernet and Fibre Channel networked disk drive arrays can provide. EMC has seen that there is a need for mainstream enterprise-class data centre I/O speed and flash dash is the way to get it. ®