IBM FlashSystem 840 for Legacy-free Flash

Flash storage is at an interesting place and it’s worth taking the time to understand IBM’s new FlashSystem 840 and how it might be useful.

A traditional approach to flash is to treat it like a fast disk drive with a SAS interface, and assume that a faster version of traditional systems are the way of the future. This is not a bad idea, and with auto-tiering technologies this kind of approach was mastered by the big vendors some time ago, and can be seen for example in IBM’s Storwize family and DS8000, and as a cache layer in the XIV. Using auto-tiering we can perhaps expect large quantities of storage to deliver latencies around 5 millseconds, rather than a more traditional 10 ms or higher (e.g. MS Exchange’s jetstress test only fails when you get to 20 ms).

No SSDs 3

Some players want to use all SSDs in their disk systems, which you can do with Storwize for example, but this is again really just a variation on a fairly traditional approach and you’re generally looking at storage latencies down around one or two millseconds. That sounds pretty good compared to 10 ms, but there are ways to do better and I suspect that SSD-based systems will not be where it’s at in 5 years time.

The IBM FlashSystem 840 is a little different and it uses flash chips, not SSDs. It’s primary purpose is to be very very low latency. We’re talking as low as 90 microseconds write, and 135 microseconds read. This is not a traditional system with a soup-to-nuts software stack. FlashSystem has a new Storwize GUI, but it is stripped back to keep it simple and to avoid anything that would impact latency.

This extreme low latency is a unique IBM proposition, since it turns out that even when other vendors use MLC flash chips instead of SSDs, by their own admission they generally still end up with latency close to 1 ms, presumably because of their controller and code-path overheads.

FlashSystem 840

  • 2u appliance with hot swap modules, power and cooling, controllers etc
  • Concurrent firmware upgrade and call-home support
  • Encryption is standard
  • Choice of 16G FC, 8G FC, 40G IB and 10G FCoE interfaces
  • Choice of upgradeable capacity
Nett of 2-D RAID5 4 modules 8 modules 12 modules
2GB modules 4 TB 12 TB 20 TB
4GB modules 8 TB 24 TB 40 TB
  • Also a 2 TB starter option with RAID0
  • Each module has 10 flash chips and each chip has 16 planes
  • RAID5 is applied both across modules and within modules
  • Variable stripe RAID within modules is self-healing

I’m thinking that prime targets for these systems include Databases and VDI, but also folks looking to future-proof their general performance. If you’re making a 5 year purchase, not everyone will want to buy a ‘mature’ SSD legacy-style flash solution, when they could instead buy into a disk-free architecture of the future.

But, as mentioned, FlashSystem does not have a full traditional software stack, so let’s consider the options if you need some of that stuff:

  • IMHO, when it comes to replication, databases are usually best replicated using log shipping, Oracle Data Guard etc.
  • VMware volumes can be replicated with native VMware server-based tools.
  • AIX volumes can be replicated using AIX Geographic Mirroring.
  • On AIX and some other systems you can use logical volume mirroring to set up a mirror of your volumes with preferred read set to the FlashSystem 840, and writes mirrored to a V7000 or (DS8000 or XIV etc), thereby allowing full software stack functions on the volumes (on the V7000) without slowing down the reads off the FlashSystem.
  • You can also virtualize FlashSystem behind SVC or V7000
  • Consider using Tivoli Storage Manager dedup disk to disk to create a DR environment

Right now, FlashSystem 840 is mainly about screamingly low latency and high performance, with some reasonable data center class credentials, and all at a pretty good price. If you have a data warehouse, or a database that wants that kind of I/O performance, or a VDI implementation that you want to de-risk, or a general workload that you want to future-proof, then maybe you should talk to IBM about FlashSystem 840.

Meanwhile I suggest you check out these docs:

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2 Responses

  1. There are many flash chips inside any SSD module from any vendor. IBM didn’t do anything new. NIMBUS really innovates with DCA Distributed Cash Architecture, which dispenses external batteries (used on IBM) and cache controller/mirroring.

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