Dell EqualLogic FS7500 Technical Manual page 13

The caching effect of the FS7500 is also evident when looking at Figure 4, where we see that file I/O
clients have a slight performance advantage over the block clients. Furthermore, when we examined
the data from SAN HQ, it showed that the total number of I/Os actually completed by the storage
system for NFS clients was slightly less than the total number of I/Os from all block clients, again
indicating the beneficial effects of caching on the FS7500 system.
Figure 3: 6 - Array Shared Pool, Block and File I/O Comparison
Figure 4 shows the results when the same scaling test was run, except the block and file data were in
separate pools. In this case, overall file I/O performance was lower than it was in the shared pool, but
the overall block I/O is greater than when it shared the pool with the file I/O (as shown in Figure 3).
This is due to the way volumes are load balanced across arrays. Under normal conditions, a volume on
an EqualLogic PS Series iSCSI SAN may be distributed across up to three of the PS Series arrays. When
the pool is limited to three arrays, and contains only the volumes for the NAS File System, the volumes
that make up the NAS reserve will span the same physical disks. Therefore, any CIFS or NFS workloads
will also be limited to the maximum number of IOPS that the three arrays can deliver. When the single
pool was expanded to six arrays, each of our two NAS volumes automatically balanced exclusively
across three of the six arrays. The first NAS volume is on the first 3 arrays, and the second NAS volume
is on the remaining three arrays. This is expected behavior for the SAN as long as adequate free space
is available in the pool.
BP1016 9
Integrating the Dell EqualLogic FS7500 into an Existing SAN