Why use snap reserve in a flexvol?

[MSANDONASSGA]

Is there any reason to define snap reserve space in a "thick" provisioned flexvol?  

In our PROD environment we use autosize (mode: grow) and have autodelete configured for snapshots.  By default we create our flexvols with 20% snap reserve.  I'm noticing that this is resulting in a lot of unused space.

I have found that 0% snap reserve is recommended for "thin" provisioned volumes and for volumes that contain LUNs.  

Thank you.

[moep]

The snapshot reserve has an impact on the size visible to the user.

Let's say the user requested 100GB space.

- You provide a 100GB volume without snapshot reserve. The user sees 100GB free space. The User allocates 20GB, another 10GBs are allocated by snapshots. Now the user sees 70GB free space, even though he only allocated 20GB by himself.

- You provide a 110GB volume with 10% snapshot reserve. The user sees 100GB free space. The User allocates 20GB, another 10GBs are allocated by snapshots. Now the user sees 80GB free space.

[MSANDONASSGA]

Hi Moep.

Yes.  I understand the impact of setting a snap reserve.  My question was more about if there's any "benefit" - performance or other for setting it or a negative impact for not setting it.

What I've learned subsequent to my posting is that there's no really benefit to enabling it other than setting aside space that can only be used for snap data.  

From a management and storage use optimization, it's my opinion that 0% snap reserve is the way to go.  When I look at utilization, data is data to me.  I don't care if it's snap data or active filesystem data.  For reporting puposes, I like to not have to break out usage as combo of snap data + file system data. 

So for me, it's 0% snap reserve in 99% of cases.

[aborzenkov]

Snap reserve does not set aside anything. It changes available space that is reported to clients. It is intended to reduce confusion when deleting file does not increase available space.