In July last year I blogged about a brief history of XIV.
At the risk of getting over excited, some of the achievements of the IBM XIV have been truly remarkable:
- There are 59 Clients with more than 1 PB each of usable XIV capacity
- There are 16 Clients with more than 2 PB each of usable XIV capacity
I am sure some competitors will find larger numbers to try to drown out this achievement, but the point is this: These are FANTASTIC numbers. It shows that despite all the FUD, the XIV is a success for IBM and a success for IBM’s customers.
So at the time of the Gen3 release, IBM made no secret of the fact that they planned to add the option of SSD as a read cache layer. In fact each and every Gen3 shipped so far has the mounting and attachment hardware needed to support those SSDs.
Now with release 3.1 IBM turns that promise into a reality.
So… to answer some possible questions:
How can I get some of this SSD goodness?
Order the feature! For existing machines, IBM will need to update the firmware of your XIV Gen3 (non-disruptively) to add SSD support. There will also be an updated version of the XIV GUI. Once those are in place, an IBM Service Representative will add an SSD to each interface module. They just slide into the mounting kit on each Gen3 module, and are then brought on-line as a group. No module replacements (or phasing in and out of modules) are necessary and no data needs to be redistributed at any point. All of this will thus be completed without interruption to your operations.
How much read cache will I get?
Each XIV Gen3 Module already has 24 GB of server RAM. Since an XIV can vary from 6 to 15 modules (based on capacity), that gives you between 144 GB and 360 GB of server RAM to provide read and write cache. If you add the SSD option you will get a 400 GB SSD per module. This means we get between 2.4 TB to 6 TB of additional read cache (depending on module count). The SSDs are not used as write cache.
What administration will I need to perform?
How about none? This is XIV: it’s all about making it simple. It’s no surprise that practically every IBM Storage device now uses the XIV GUI. These guys wrote the book on making things easy to use.
But seriously, no administration? Well… there are two things you may want to do:
- Check how many SSD based read hits you are getting (versus memory based read hits). It’s always nice to see just how effective these SSDs are proving themselves to be.
- Turn SSD read caching off or on at a per volume level (by default it is on for all volumes). I don’t anticipate many clients will need or want to do this, but the option is there and it is very easy to do.
Won’t these SSDs wear out or slow down over time?
These are the two great fears of SSD… and XIV development has combined their art with some great work from IBM Research to make sure this is not an issue. The way data is written out to the SSD is handled in a very sophisticated manner. The end result will be consistent and predictable performance with a very long operational life. I will give you more details about exactly how this is done in a future post.
What happens if one of these SSD fails?
Because the SSD is not used as write cache, no data can be lost. Data in memory cache is de-staged by that module to both SAS disk and asynchronously to SSD (although not all data will necessarily go to SSD). So there are no bottlenecks and there is no risk. The other modules will keep using their SSDs and IBM will replace the failed SSD non-disruptively.
What sort of performance improvement will I see?
Depending on application and data patterns you should see your IOPS more than double. A three times improvement is quite possible. Response times could drop by more than two-thirds. In many ways these are obvious results.
IBM intend to demonstrate using industry standard benchmarks what the performance of an XIV Gen3 with SSD will be. I can tell you these numbers are going to be very impressive. Watch this space.
Is that it? Any thing else in this release?
Release 3.1 (more correctly known as firmware version 11.1 as per here) also adds:
- The ability to mirror between Generation 2 and Gen3 XIVs.
- All the base support for IPv6 is now in place (although there are still some certification tests to complete)
- Improvements to system thresholds (such as maximum pool size)
- GUI enhancements (mainly to add panels for the SSD cache)
- A new iPhone app (in addition to the existing iPad app)
It’s like Christmas in February.