Yellow Bricks

by Duncan Epping

ssd

600GB write buffer limit for VSAN?

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Write Buffer Limit for VSANI get this question on a regular basis and it has been explained many many times, I figured I would dedicate a blog to it. Now, Cormac has written a very lengthy blog on the topic and I am not going to repeat it, I will simply point you to the math he has provided around it. I do however want to provide a quick summary:

When you have an all-flash VSAN configuration the current write buffer limit is 600GB. (only for all-flash) As a result many seem to think that when a 800GB device is being used for the write buffer that 200GB will go unused. This simply is not the case. We have a rule of thumb of 10% cache to capacity ratio. This rule of thumb has been developed with both performance and endurance in mind as described by Cormac in the link above. The 200GB that is above the 600GB limit of the write buffer is actively used by the flash device for endurance. Note that an SSD usually is over-provisioned by default, most of them have extra cells for endurance and write performance. Which makes the experience more predictable and at the same time more reliable,  the same applies in this case with the Virtual SAN write buffer.

The image at the top right side shows how this works. This SSD has 800GB as advertised capacity. The “write buffer” is limited to 600GB however the white space is considered “dynamic over provisioning” capacity as it will be actively used by the SSD automatically (SSDs do this by default). Then there is an additional x % of over provisioning by default on all SSDs, which in the example is 28% (typical for enterprise grade) and even after that there usually is an extra 7% for garbage collection and other SSD internals. If you want to know more about why this is and how this works, Seagate has a nice blog.

So lets recap, as a consumer/admin the 600GB write buffer limit should not be a concern. Although the write buffer is limited in terms of buffer capacity, the flash cells will not go unused and the rule of thumb as such remains unchanged: 10% cache to capacity ratio. Lets hope this puts this (non) discussion finally to rest.

Startup News Flash part 17

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Number 17 already… A short one, I expect more news next week when we have “Storage Field Day”, hence I figured I would release this one already. Make sure to watch the live feed if you are interested in getting the details on new releases from companies like Diablo, SanDisk, PernixData etc.

Last week Tintri announced support for the Red Hat Enterprise Virtualization platform. Kind of surprising to see them selecting a specific linux vendor to be honest, but then again it probably also is the more popular option for people who want full support etc. What is nice in my opinion is that Tintri offers the exact same “VM Aware” experience for both platforms. Although I don’t see too many customers using both VMware and RHEV in production, it is nice to have the option.

CloudVolumes, no not a storage company, announced support for View 6.0. CloudVolumes developed a solution which helps you manage applications. They provude a central management solution, and the option to distribute and elimate the need for streaming / packaging. I have looked at it briefly and it is an interesting approach they take. I like how they solved the “layering” problem by isolating the app in its own disk container. It does make me wonder how this scales when you have dozens of apps per desktop, never the less an interesting approach worth looking in to.

Startup News Flash part 16

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Number 16 of the Startup News Flash, here we go:

Nakivo just announced the beta program for 4.0 of their backup/replication solution. It adds some new features like: recovery of Exchange objects directly from compressed and deduplicated VM backups, Exchange logs truncation, and automated backup verification. If you are interested in testing it, make sure to sign up here. I haven’t tried it, but they seem to be a strong upcoming player in the backup and DR space for SMB.

SanDisk announced a new range of SATA SSDs called “cloudspeed”. They released 4 different models with various endurance levels and workload targets, of course ranging in sizes from 100GB up to 960GB depending on the endurance level selected. Endurance level ranges from 1 up to 10 full drive writes per day. (Just as an FYI, for VSAN we recommend 5 full drive writes per day as a minimum) Performance numbers range between 15k to 20k write IOps and 75 to 88K read IOps. More details can be found in the spec sheet here. What interest me most is the FlashGuard Technology that is included, interesting how SanDisk is capable of understanding wear patterns and workloads to a certain extend and place data in a specific way to prolong the life of your flash device.

CloudPhysics announced the availability of their Storage Analytics card. I gave it a try last week and was impressed. I was planning on doing a write up on their new offering but as various bloggers already covered it I felt there was no point in repeating what they said. I think it makes a lot more sense to just try it out, I am sure you will like it as it will show you valuable info like “performance” and the impact of “thin disks” vs “thick disks”. Sign up here for a 30day free trial!

Startup News Flash part 15

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Number 15 of the Startup News Flash… What happened in the world of (storage / flash related) startup’s in the last couple of weeks? Not too much news, but I felt it was worth releasing anyway as other wise the below would be really old news.

One of the most interesting BC/DR startups of the last couple of years, if you ask me, just announced a new round of funding: 100 million. Investors include North Bridge, Greylock, Advanced Technology Ventures, Andreessen Horowitz, and Technology Crossover Ventures. For those who don’t know Actifio… Actifio offers what is commonly referred to as a “Data Copy Management” solution. It could be described as a solution which sits in between your storage solution and your hypervisor and can do things like: backup, cloning, replication, archiving etc. Really neat solution, with a brilliant super simple UI. Worth checking out if you are looking to improve your business continuity story!

A while back I wrote an introduction to SoftNAS. When doing that review there was one thing that stood out to me and that was that SoftNAS didn’t have a great availability story. I spoke with Rick Brady about that and he said that it would be one of the first things they would try to tackle in an upcoming release. In the just announced release SoftNAS introduces Snap HA. Snap HA provides an “active / passive” solution where when an issue arises ownership is transferred to the “passive” node which then of course becomes “active”. More details can be found in this blog post by Rick Brady. Awesome work guys!

Startup News Flash part 14

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Part 13 of the Startup News Flash… Hopefully not an unlucky one for the startups featured. Just a short one considering I am in Vietnam and away ‘from work’ for the last 2 weeks.

A3Cube is a startup which came out of stealth recently and announced as they call it a ‘brain inspired’ data plane encapsulated in a NIC designed to bridge supercomputing benefits to the enterprise. The core of their solution is called Ronnie Express. They aim is to eliminate the I/O performance gap between CPU power and data access performance for HPC, Big Data and data center applications. A3CUBE’s In-Memory Network technology allows direct shared non-coherent global memory across the entire network, enabling global communication based on shared memory segments and direct load/store operations between the nodes. Basically a server “interconnect” solutions for lrge scale. They took the word “scale” serious by the way and can go up to 64,000 nodes. For more details, I highly recommend to read this excellent article by Enrico.

Infinio just announced Infinio Accelerator 1.2. This new version of the Infinio Accelerator now supports vSphere 5.5. Useful to know for those who have a home lab, Infinio is running a limited-time offer of free non-expiring licenses for test labs. Hit their website to find out more.