Tag Archives: block count

VMFS UNMAP switches block count

A recent question I got about my UNMAP PowerCLI script was it says it was using a certain block count but when I looked at the log it was using 200. Why?

Well I blogged before about why a given UNMAP process might revert to the default block count of 200 here. Essentially, if you indicate a block count larger than 1% of the free space of the VMFS ESXi will revert it to 200. Or if the VMFS is more than 75% full it will always override the block count back down to 200. Continue reading VMFS UNMAP switches block count

UNMAP Block Count Behavior Change in ESXi 5.5 P3+

I recently was doing some troubleshooting for a customer that was using my UNMAP PowerCLI script and discovered a change in ESXi 5.5+ UNMAP. The issue was that the script was taking quite a while to complete. After some logic optimizations and increasing timeouts the script was sped up a bit and less timeout errors occurred, but a bunch of the UNMAP operations were still taking a lot longer than expected. Eventually we threw our hands up and said it was good enough. A bit more recently, I was testing a 3rd party UNMAP tool and ran into similar behavior so I dug into it a bit more and found some semi-unexpected changes in how UNMAP works, specifically the behavior when leveraging non-default block iteration counts. Continue reading UNMAP Block Count Behavior Change in ESXi 5.5 P3+

Deeper dive on vSphere UNMAP block count with Pure Storage

I posted a week or so ago about the ESXCLI UNMAP process with vSphere 5.5 on the Pure Storage FlashArray here and came up with the conclusion that larger block counts are highly beneficial to the UNMAP process. So the recommendation was simply use a larger block count than the default to speed up the UNMAP operation, something sufficiently higher than the default of 200 MB. I received a few questions about a more specific recommendation (and had some myself) so I decided to dive into this a little deeper to see if I could provide some guidance that was a little more concrete. In the end a large block count is perfectly fine–if you want to know more details–read on!


Continue reading Deeper dive on vSphere UNMAP block count with Pure Storage