I have a question on the best practices minimal free space in multi-tiered FAST VP pool. On FLARE 31 it was 10%, then with FLARE 32 release there was a KB article that changed it to 5% due to some changes FAST VP autotiering operation. Is it now back at 10% with FLARE 33? What is the history behind this?
Thanks for the help,
In Release 31, FAST VP would not relocate onto RAID Groups with less than 10% free space and so the recommendation was for the Pool to have at least 10% free space in total. The FAST VP relocation behaviour changed in Release 32 for VNX and Release 33 for VNX2, so that FAST VP would still relocate slices when there was less than 10% free space in the pool and would try to keep the free space evenly distributed between the RG. However, as the amount of free space drops, the efficiency of the relocations will decrease and so the best practice guides specify a minimum free space of 5% for File Pools and a general recommendation of 10% free space for Block. This is assuming that the Pool is not over-subscribed with thin LUNs, because in that case, having a lot more free space would be advisable.
The short answer is though, at current levels of VNX OE, so long as you have at least 5% free space in the Pool, FAST VP should be able to perform its relocations efficiently and that is the recommended minimum free space.
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