![\"Thick](\"http:\/\/rmohan.com\/wp-content\/uploads\/2016\/04\/Thick-thin.png\")
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<\/p>\n The VMware Thick Eager Zeroed Disk vs the Lazy Zeroed Thick disk in write performance.<\/strong><\/p>\n What is the potential write performance difference between the VMware virtual disks: Thick Lazy Zeroed, Thick Eager Zeroed and Thin provisioned types? This has been discussed for many years and there are many opinions regarding this, both in terms of test vs real life write behavior as well as test methods. There is also important factors as storage effiency, migration times and similar to this, however I will in this article try to make the potential \u201cfirst write\u201d impact more easy to evaluate.<\/p>\n Before the virtual machine guest operating system can actually use a virtual disk some preparations has to be accomplished by the ESXi host. The main tasks that has to be done for each writable part of a virtual disk is that the space has to be allocated <\/em>on the datastore and the specific disk sectors on the storage array has to be safely cleared <\/em> (\u201czeroed\u201d) from any previous content.<\/p>\n In short, this is done in the following way:<\/p>\n Thin<\/strong>: Allocate and zero on first write There are some published performance tests between these three disk types often using the standard tool IOmeter. There is however a potential flaw to these tests, caused by the fact that before<\/em> IOmeter starts the actual test it will create a file (iobw.tst) and write data to each part of that file \u2013 which at the same time causes ESXi to zero out these blocks on the storage array. This means that it is impossible to use IOmeter output data to spot any write performance differences between the three VMware virtual disk types, since the potential difference in write performance will already be nullified when the IOmeter test actually begins.<\/p>\n When the difference will only be in the very first write from the Virtual Machine across the virtual disk sectors a way to simulate this is to force a massive amount of writes over the whole disk area and note the time differences. This is of course not how most applications work in the sense that it is uncommon to do all writes in one continuous stream and instead the \u201cfirst-writes\u201d with ESXi zeroing is likely to be spread over a longer period of time, but sooner of later each sector that is used by the guest operating system has to be zeroed.<\/p>\n <\/p>\n A way to simulate large amounts of writes could be done from using the standard Windows format tool which, despite some popular belief, actually erases the whole disk area if selecting a \u201cfull\u201d \/ non-quick format. In real life there is not much specific interest how fast a partition format is done in itself, however in this test the format tool is used just to create a massive amount of \u201cfirst-writes\u201d.<\/p>\n <\/p>\n This test case uses a VM with Windows 2012 R2 which was given three new virtual hard disks of 40 GB each, where there was one Eager, one Lazy and one Thin. Each disk was then formatted with NTFS, default allocation unit, no compression, but with the non-quick<\/strong> option.<\/p>\n <\/p>\n<\/a><\/p>\n
\nThick Lazy<\/strong>: Allocate in advance and zero on first write
\nThick Eager<\/strong>: Allocate and zero in advance<\/p>\n<\/a><\/p>\n<\/a><\/p>\n