how much % reserve for snapshot?

A good rule of thumb for snapshot reserve is to set the reserve to an initial value and observe how many snapshots you can keep over a specified time period under a normal workload.  If you are using schedules to create snapshots, allow the schedule to run for several days.

To obtain an initial value for a volume's snapshot reserve, you must estimate the amount and type of volume writes and the number of snapshots you want to keep.

Example:

If you expect few writes or writes that are concentrated in a narrow range of logical blocks, and you want to keep only a few snapshots, start with a value of 30-40%.

If you expect many writes or writes that are random across a wide range of logical blocks, and want to keep more than a few snapshots, start with a value at 100%.

If snapshots are deleted before you reach the desired number of snapshots, increase the snapshot reserve percentage. If you reach the desired number of snapshots without consuming most of the free snapshot reserve, decrease the snapshot reserve percentage. Continue to monitor snapshot reserve and make adjustments as needed

Also see the KB article titled “ARRAY: How snapshot reserve space is allocated and used” at the EqualLogic support site. support.equallogic.com/.../solutions.aspx (login required), select Resources> KnowledgeBase, search for “Snapshot Reserve”

- Joe

ok so I got a 500gb lun. with 20% snap reserve.

under space tab on the volume settings

It says 421.79 gb in use

free 78.22 free

the in use space includes both snapshot and data?

what does the use thin provision check box do? can you give an example

The thin provisioning checkbox enables thin provisioning.

Some info on thin provisioning can be found here: en.wikipedia.org/.../Thin_provisioning.

Snapshot reserve doesn't come out of the 500GB (volume); it uses space outside of the 500GB volume (so in your case you have a 500GB volume and 100GB snapshot reserve (for this volume). This means it uses 600GB from your storage pool.

That's because of the way VMware reserves the diskspace, but doesn't write the whole (empty) vmdk file to disk. It's kind of like a 'quick format' (in Windows) in the sense that a quick format doesn't clear every single sector on the disk; it only rewrites the first few sectors. The SAN can see that not 395GB of data has really been written to disk (yet), but VMware knows that you may at one point do this, so it 'reserves' the space.

The opposite can happen too; if you were to delete or move all the VMs off the volume, the SAN will now still report 198.72GB in use, even though VMware will say there's 499.75GB (or close to that) available. This is because VMware at one point wrote some data to disk there and the SAN sees that the data is still there (but VMware has marked the disk area as available for new data). It's similar to how Windows 'deletes' files; it doesn't really delete them, it just marks the space as available for new data. The SAN just can't tell the difference (it doesn't know about files; it just knows about blocks of data).

he amopunt of used space on the equalogic on the volume shows

In-Use: 198.72GB

but in vsphere it shows

395.36GB Used out of 499.75GB volume

why is that?