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mikefoley
VMware Employee
VMware Employee

Growable disks, fragmentation and host (NTFS) block/cluster size

In VMFS, the default block/cluster/allocation size is 1MB. When running VMware Workstation on an XP host, the virtual machines are probably getting created on a disk with the default 8k block/cluster/allocation size. When using growable disks, this seems to exacerbate the fragmentation of the VMDK files and leads to disk thrashing, especially on laptops running VMware Workstation.

My question: Has any performance work/testing been done with creating an NTFS partition (seperate from the OS partition of course) for the VM's with a 1MB block/cluster/allocation size? Primarily around lessening the fragmentation of the VMDK's.

Any thoughts? I haven't tried doing this, but before I did, I thought I'd ask. Smiley Happy

thanks,

mike

mike
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Peter_vm
Immortal
Immortal

Actually for NTFS default allocation unit is 4KB.

With preallocated disks this problem does not occur and data is read most often in 64KB blocks anyways.

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mikefoley
VMware Employee
VMware Employee

You're right, 4kb. However, the problem isn't reading 64k, it's the writes with a growable disk or snapshots that cause the fragmentation. (IMHO, I'd be glad to be proved otherwise)

The situation here is that we want to ship out VM's to sales engineers with multiple snapshots. We use growable disks because the space is smaller, but the performance gets prettty crappy after being used for a while.. In addition, they create VM's using growable disks because they are limited in physical disk space. My hope was that with 1MB cluster size, I'd get similar performance that I'd get with VMFS.

I'd love to have a library of differences/deduped files that they could apply on top of cloned templates to re-create demos. In an ideal world, we'd have a desktop or lite version of Avamar that would de-dupe the VM's. I've looked at Prowess and vPackager, but the cost is kinda high and doesn't fit with what we need to do. (Lots of VM's and demos)

mike

RSA/EMC

mike
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oreeh
Immortal
Immortal

Since the default grainSize is 64KB the "optimal" NTFS cluster size should be 64KB as well.

continuum
Immortal
Immortal

Make sure you have a defragmentation tool that can handle the block-size you select. If not - you will loose more than you gain by tweaking blocksize

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mikefoley
VMware Employee
VMware Employee

Thanks to the input I've recieved so far, I've come to the conclusion that mucking with the NTFS cluster size is probably not worth the trouble.

Thanks guys,

mike

mike
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