4kn & 512e vSphere Support

Just a reminder for people not to create volumes with a 4K sector size with vSphere or VSAN, allot of the newer firmware revisions are now allowing 4K sector sizes for example Dell EqualLogic.

See the below screenshot as an example although the 512byte sector size is the default the adventurous or hungover IT admin amongst us may end up going with the 4K option without considering the consequences.

Screenshot 2015-09-02 10.20.28

VMware have made their support statement quite clear on this over the last few months but I thought I would repost this for the benefit of others who might not of seen this KB.

What are 4K Native and 512e drives?
Industry standard disk drives have been using a native 512 bytes sector size. However, due to the increasing demand for larger capacities, the storage industry introduced new advanced formats, which are 512-byte emulation (512e) and 4KB Native (4Kn).

4Kn is the advanced format in which the physical sectors and logical sectors are both 4,096 bytes in size.

512e is the advanced format in which the physical sector size is 4,096 bytes, but the logical sector size emulates 512 bytes sector size.

This table compares Native 512-byte sectors to the new advanced formats:

Format Logical Sector Size Physical Sector Size
512n 512 512
512e 512 4,096
4Kn 4,096 4,096

Does current GA version of vSphere and VSAN support 4K Native drives?

No. 4K Native drives are not supported in current GA releases of vSphere and VSAN.

Does current GA version of vSphere and VSAN support 512e drives?

No. 512e drives are not supported with the current versions of vSphere and VSAN due to potential performance issues when using these drives.

For further reading please see VMware KB2091600

Latency What Latency – Nimble Storage

Having just completed a storage/ VMware migration from 4 x Dell Equallogics to a single Nimble CS300 (48TB 2.4TB Cache 1GB iSCSI) I just wanted to share with you my experience.

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The firm runs a number of highly transactional Microsoft SQL servers which accepts data from the likes of Compare the Market and GoCompare. They have approximately 75 vm’s and also a small VDI environment running on the Nimble. Unsurprisingly the Nimble handles all this without breaking in to a sweat, but that’s to be expected right ?

So why do we get so much performance from a 3U box with 12 SATA disks and 4 SSD’s; quite simply CASL

CASL is a CPU-driven storage architecture, so write performance is no longer dependent on spindle speed or spindle count. What’s more, CASL dramatically increases the usable capacity of disk and flash through compression and its unique sequential data layout.

This document provides a great overview on CASL for those that want to know more.

So after the environment had bedded in I took a look at the Nimble interface to see what the steady state IOP and latency figures were for this environment, bearing in mind we have several highly transactional SQL servers, 75 vm’s and a small virtual desktop environment all running on this box, lets take a look below.

IOP figures for an average working day

Screenshot 2015-08-26 21.53.49(2)

  • Random Read: 881 IOPS
  • Sequential Read: 1931 IOPS
  • Random Write: 580 IOPS
  • Sequential Write: 180 IOPS

Latency figures for an average working day ( 1GB iSCSI Network)

Screenshot 2015-08-26 21.53.49

  • Read Latency 0.42msec
  • Write Latency 0.19msec

Pretty impressive figures considering the blended workload, this is about the 11th Nimble I have installed and I am always impressed with the performance of these arrays.