VMFS : Virtual Machine File System
In my previous post i have talked about something basic about VMware Storage. Those are the major technologies which will be used by VMware. What ever the technology that sits behind, but the final target is to provide maximum uptime using enterprise future provided by VMware. Storage plays a key role in this part. Not only the storage, the file system which is created on that storage also plays an important role.
VMware uses a file system called VMFS, which has extensive support to the clustering in VMware Environment. And also supports futures like VMotion, DRS, RDM, Snapshots etc. Here i have provided some of the Features and Limitations of Virtual Machine File Systems. This is used by all the virtual machines, and apart from this every virtual machine has its own file system like Windows VM has NTFS, Linux VM has ext2/3 FS etc. So in conclusion i can say like a file system which gives support to another file system.
Allows access by multiple ESX Servers at the same time by implementing per-file locking. SCSI Reservations are only implemented when LUN meta data is updated (e.g. file name change, file size change, etc.)
Add or delete an ESX Server from a VMware VMFS volume without disrupting other ESX Server hosts.
LVM allows for adaptive block sizing and addressing for growing files allows you to increase a VMFS volume on the fly (by spanning multiple VMFS volumes)
With ESX/ESXi4 VMFS volumes also can be expanded using LUN expansion
Optimize your virtual machine I/O with adjustable volume, disk, file and block sizes.
Recover virtual machines faster and more reliably in the event of server failure with Distributed journaling.
Can be shared with up to 32 ESX Servers.
Can support LUN's with max size of 2TB and a max VMFS size of 64 TB as of version 4 (vSphere).
"There is a VMFS-3 limitation where each tree of linked clones can only be run on 8 ESX servers. For instance, if there is a tree of disks off the same base disk with 40 leaf nodes in the tree, all 40 leaf nodes can be simultaneously run but they can only run on up to 8 ESX hosts."
VMFS-3 limits files to 262,144 (218) blocks, which translates to 256 GB for 1 MB block sizes (the default) up to 2 TB for 8 MB block sizes.
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