What’s New in Purity 5.1: WRITE SAME Handling Improvement

In Purity 5.1 there were a variety of new features introduced on the FlashArray like CloudSnap to NFS or volume throughput limits, but there were also a variety of internal enhancements. I’d like to start this series with one of them.

VAAI (VMware API for Array Integration) includes a variety of offloads that allow the underlying array to do certain storage-related tasks better (either faster, more efficiently, etc.) than ESXi can do them. One of these offloads is called Block Zero, which leverages the SCSI command called WRITE SAME. WRITE SAME is basically a SCSI operation that tells the storage to write a certain pattern, in this case zeros. So instead of ESXi issuing possibly terabytes of zeros, ESXi just issues a few hundred or thousand small WRITE SAME I/Os and the array takes care of the zeroing. This greatly speeds up the process and also significantly reduces the impact on the SAN.

WRITE SAME is used in quite a few places, but the most commonly encountered scenarios are: