With the release of VSAN 6.0, and the new all-flash configuration (AF-VSAN), I have received a number of queries around our 10% cache recommendation. The main query is, since AF-VSAN no longer requires a read cache, can we get away with a smaller write cache/buffer size?
Before getting into the cache sizing, it is probably worth beginning this post with an explanation about the caching algorithm changes between version 5.5 and 6.0. In VSAN 5.5, which came as a hybrid configuration only with a mixture of flash and spinning disk, cache behaved as both a write buffer (30%) and read cache (70%). If a read request was not satisfied by the cache, in other words there was a read cache miss, then the data block was retrieved from the capacity layer. This was an expensive operation, especially in terms of latency, so the guideline was to keep your working set in cache as much as possible. Since the majority of virtualized applications have a working set somewhere in the region of 10%, this was where the cache size recommendation of 10% came from. With hybrid, there is regular destaging of data blocks from write cache to spinning disk. This is a proximal algorithm, which looks to destage data blocks that are contiguous (adjacent to one another). This speeds up the destaging operations.
In Virtual SAN version 6.0, VMware introduced support for an all-flash VSAN. In other words, both the caching layer and the capacity layer could be made up of flash-based devices such as SSDs. However, the mechanism for marking some flash devices as being designated for the capacity layer, while leaving other flash devices as designated for the caching layer, is not at all intuitive at first glance. For that reason, I’ve included some steps here on how to do it.
As many of you are aware, I was at VMworld in San Francisco last week. I wrote a number of articles about some VMware storage announcements, such as EVO:RAIL, VAIO and VVols. However there were, as usual, quite a number of storage vendors at this years conference. One of the vendors that I really want to learn more about was Kaminario, an all flash array vendor that I’d heard a lot of things about. I had the pleasure of spending some time at the Kaminario booth with Shai Maskit who is a senior Product Manager with Kaminario. I posed my usual set of questions to learn a bit more about their AFA products. Continue reading →
On a recent trip to VMware in Palo Alto, I found some time to visit with a good pal of mine, Vinay Gaonkar, who is now the Product Manager for XtremIO over at EMC. Vinay used to be a storage PM at VMware (he worked on the initial phases of VVols), and we worked together on a number of storage items in various vSphere releases. It’s been almost 2 years since I last spoke to the XtremIO folks (VMworld 2012 in fact, when the product still had not become generally available), so I thought that this would be a good time to catch up with them, as we are in the run up to VMworld 2014.
I’m sure Frank Denneman will need no introduction to many of you reading this article. Frank & I both worked in the technical marketing organization at VMware, before Frank moved on to PernixData last year and I moved to Integration Engineering here at VMware. PernixData FVP 1.0 released last year, and I did a short post on them here. I’d seen a number of people discussing new FVP features in the community, especially after PernixData’s co-founder Satyam’s presentation at Tech Field Day 5 (#TFD5). I decided to reach out to Frank, and see if he could spare some time to revisit some of the new features that PernixData is planning to introduce. Fortunately, he did. I started by asking Frank about how PernixData is doing in general, before moving onto the new bits.
Pure Storage are all over the news at the moment. They just secured another round of funding (225 million to be precise), and are now valued at over 3 billion. You can read more about that here. However, even before this announcement, I had already arranged to have a catch up chat with Pure’s primary evangelist (and a good pal of mine), Vaughn Stewart. I was surprised to see that it had been 18 months since I last did a piece on Pure so I really did want to see what changes they had made in the meantime as there were a few vSphere interoperability pieces still to be completed when we last spoke.
I watched a very cool demonstration this morning from the All Flash Array vendor, SolidFire. I spoke with SolidFire at the end of last year, and did a blog post about them here. One of the most interesting parts of our conversation last year was how SolidFire’s QoS feature and VMware’s Storage I/O Control (SIOC) feature could inter-operate. In a nutshell, QoS work at the datastore/volume layer whereas SIOC deals with the VM/VMDK layer. Last week, Aaron Delp and Adam Carter of SolidFire did an introduction to QoS, both on vSphere and on the SolidFire system. And they also did one of the coolest demos that I’d seen in some time, namely how they have managed to get SIOC and QoS to work in tandem.