We ordered a new SAN from EMC. The capacity is 9TB. Now we like to create one single LUN with all the 9TB. I read something about SCSI reservation problems on big LUN`s. On this LUN should run 40 VM`s in the future with DB Applications.
The best way to figure out your LUN size is to calculate your throughput first and then capacity second. For example you may want to carve out a 100 GB LUN for a database that has a lot of I/O and you'll just have that one VM make use of the volume. Smaller LUN's are safer (lower risk of getting it wrong) but if you calculate your IO correctly larger LUNs are fine.
Correct, you can add extents to the LUN. Each LUN is limited to 2TB. Each VMFS volume can have 32 extents. So your VMFS volume can be 64 TB's. Each extent is 2TB's. Any file must reside on a single extent, so is limited to 2TB's.
Charles Killmer, VCP
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I want to bring up Duncan's earlier comment again, because it is what will be a definate problem if/when you upgrade to vSphere later. Performance problems of creating a 8 TB are dependant on load, but the trouble you will run into with upgrading to vSphere if you create a VMFS of exactly 8 TB is a definate known. The LUNs should not be created any larger than 2 TB - 512Byte, so a VMFS datastore of 4 LUNs will be 4 TB - 2 KB.
There is a bug in ESX 3.5 that will allow you to create a VMFS of exactly 2 TB even though ESX can technically really only allow writing to 2 TB - 512Byte. vSphere now enforces the 2 TB -512B maximum properly which prevents direct upgrade of 2 TB volumes.
Reference the vSphere configuration maximums to properly plan for future upgrade when creating your datastore:
thanks for ur help ..
but i want to know y we have leave 512B and how esx server is using those 512 B....
But extent are similar to disks concatenation... so if you loose your first disk (or partition) you loose everything.
I prefer to use different datastore... or if you simple extent a LUN on storage side, you can use the new grow mode to expand also the VMFS datastore.
As Duncan stated 2TB-512Kb this will prevent issues when migrating to vSphere.
ESX can easily manage 256 VMFS partition and LUNs, it is not considered best practice to use extents for your VMFS partitions.
You are running the risk of data loss, if you lose a LUN from your extent you have lost the entire VMFS partition or all your VM Guests. If you have four or five separate LUNs you will only lose the Guests on that particular LUN.
The adage here is just because you can do something, does not necessarily mean it is good to do so.
Further there is no particular management overhead in having multiple LUNs attached to an ESX cluster. I would advise you to read the documentation, read the numerous posts on this site and also read some of the blog sites on VMware ESX out there.