Yellow Bricks

by Duncan Epping

Startup News Flash part 12

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First edition of the 2014 of the Startup News Flash. I expect this year to be full of announcements, new rounds of funding, new products, new features and new companies. There are various startups planning to come out of stealth this year and all play in the storage / flash space, so make sure to follow this series!

On Tuesday the 14th of January Nutanix announced a new round of funding. Series D financing is co-led by Riverwood Capital and SAP Ventures, and the total amount is $101 million. The company has now raised a total of $172.2 million in four rounds of funding and has been valuated close to $ 1 billion. Yes, that is huge. Probably one of the most successful startups of the last couple of years. Congrats to everyone involved!

Tintri announced a rather aggressive program. The Register reported it here, and it is all about replacing NetApp systems with Tintri systems. In short: “The “Virtualize More with 50% Less” Program offers 50% storage capacity and rack space savings versus currently installed NetApp FAS storage to support deployed virtualization workloads”. I guess it is clear what kind of customers they are going after and who their primary competition is. Of course there is a list of requirements and constraints which the Register already outlined nicely. If you are looking to replace your current NetApp storage infrastructure I guess this could be a nice offer, or a nice way to get more discount.. Either way, you win.

SSD and PCIe flash devices are king these days, but SanDisk is looking to change that with the announcement of the availability of the ULLtraDIMM. The ULLtraDIMM is a combination of Diablo’s DDR3 tranlation protocol and SanDisk’s flash and controllers on top of a nice DIMM. Indeed, it doesn’t get closer to your CPU then straight on your memory bus. By the looks of it IBM is one of the first vendors to offer it, as they  recently announced that the eXFlash DIMM is an option for its System x3850 and x3950 X6 servers providing up to 12.8TB of flash capacity2. Early benchmarks showed write latency around 5-10 microsecond! I bet half the blogosphere just raised their hands to give this a go in their labs!

 

Virtual SAN Datastore Calculator

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Over a week ago I wrote an article around how to size your Virtual SAN Datastore. I included an equation to help everyone who is going through the same exercise. I figured I should be able to make life even easier by creating a simple Virtual SAN Datastore calculator based on this equation.

<EDIT> VMware has launched a great calculator. My tool served as a temporary solution as there was no calculator available, now that there is I highly recommend using the official tool: http://virtualsansizing.vmware.com/ </EDIT>

Virtual SAN Read IO – cache / buffer / spindles

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I had a question around how Virtual SAN read IO is handled when data can be anywhere: read cache, write buffer, disks. On VMTN one of the engineers recently explained this. I figured I would create a quick diagram to illustrate it. Basically how it works is that VSAN will check the read cache, if the block that needs to be read is not available in the read cache it will check whether the block is in the write buffer or on disk. Simple right?

In the scenario I drew below two blocks needs to be read. Block 1 is actively served by ESXi-01 and Block 2 is actively served by ESXi-03. In the case of ESXi-01 the block resides in the read cache so it is read from the cache. In the case of ESXi-03 it is not in the read cache and neither in the write buffer, hence it is read from the magnetic disks. Do note that this is 1 virtual machine, so reads are being served from 2 hosts and depending who is actively serving IO for that block the block can reside on that host in the read cache. The host which is not actively serving IO for that block will also not place the block in the read cache! (Of course if the host which is actively serving IO for a block fails the other host will take over.)

I hope that helps.

How to remove a host from your Virtual SAN cluster

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The question “How to remove a host from your Virtual SAN cluster” has now popped up various times, so I figured I would write a short article around what the current procedure is. It is fairly straight forward to be honest, here we go:

  1. Place host in maintenance mode
  2. Delete disk group when “maintenance mode” is completed
  3. Move host out of the cluster
  4. Remove the VSAN VMkernel (not a requirement, but I prefer to clean things up)

That is it, now you can re-purpose the host for anything else.

Access Denied on wp-admin / wp-login page

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I have had this problem various times in the last 6 months on my WordPress blog. For whatever reason all of a sudden when I access my wp-admin page I receive an access denied on wp-admin / wp-login.php. Really annoying as you can imagine as it means you cannot get in to the back-end of your blog making it impossible to manage it. The blog it self is still available though when this happens so I figured I would write down the fix, as I somehow keep forgetting it.

  • FTP in to host
  • Check file permissions on wp-login.php, in my case permissions on this file are somehow magically always “00”
  • Change permissions back to 0644
  • Fixed, you should be able to login again

Simple solution, for a strange problem. If I ever find the rootcause I will post it here as well.