2009-05-11 03:33 AM
I've reduced this to 2% before, but be very careful with reducing aggr snap reserve as it gets used for a few different things. One example is semi-sync SnapMirror where it is used as a buffer.
2009-05-11 05:23 AM
If you don't have RAID syncmirror and / or a metrocluster configuration and you don't expect to use aggregate snap restores (has anyone ever used this???), you don't need snapshots on aggregate level and therefore can set the aggregate snap reserve to 0%. If you use aggregate snapshots set the snap reserve to such a level that you normally don't run of reserve space.
We are running on all our non metrocluster configurations with 0% aggregate snap reserve and no aggregate snapshots (snap sched -A <aggregate> 0) ever since we migrated to ontap 7.0.
2009-05-11 05:49 AM
Thank you Dukers,
As I know, you need to save some space for some maintenance processes like block reallocation or in case of aggr inconsistence when you need to run wafl_check.
Professional Services Engineer
2009-05-12 12:40 PM
I wouldn't go below 3% aggregate snap reserve (that does let you get back 2% from the default at least) as doing otherwise can cause data corruption issues (as well as cause issues upgrading to 7.3.x).
See this bug report as well....
There was also a general warning in the 7.3.x upgrade docs about this as well giving 3% as a minimum.
I would stay away from 0% aggregate snap reserve as I have personally had data corruption issues with this (a volume with "file" space guarantee got set to "none" silently and subsequently had some corrupted files which we didn't notice for a couple months due to some odd circumstances).
2009-05-13 02:07 AM
The bug is not about snap reserve size for the aggregate, but about free space in the aggregate. Using a snap reserve of more than 0% is only a tool to make sure nothing can ever take up all the space in an aggregate.
I always have at least 10% free in the aggregate, therefore for me this will never be an issue. But if I am wrong I would really like to know about it.
2010-02-28 11:23 PM
Hi, we always leave default 5%.
And disabling aggr snap reserve only with metrocluster configuration or when extra space needed (not best practice but...).
Best practice for us is at least 10% free space in aggregate.
2010-02-28 11:30 PM
There is no right or wrong here, just do what makes you comfortable.
If you don't use aggregate snapshots, there is no need to to reserve space in the aggregate. But some use the snap reserve as a tool to make sure there is always (enough) free space in the aggregate.