Just a quick note on possibilities available to do some bench-marking of NAS performance. Quite often Blackmagic Disk Speed Test or Intel NAS Performance Toolkit are being used for this. But there are some problems with those: first one is nice and cool but for Mac only, second is good but no longer supported by Intel as it reached its EoL.
So if you look for the other options you may use the following:
ToTu Soft LAN Speed Test – they have commercial and free versions, and promise to deliver Mac OS release soon.
NAS performance tester by Ulrik D. Hansen, absolutely free and with source code available (though it only measures read/write speed values).
I really liked this last option as it is portable and allowed me to do some quick tests against iSCSI target hosted on my Synology DS415+ (gigabit Ethernet connection; 1 drive only, no RAID, both data and header digests enabled). You may see test results below.
Using 400 Mb file:
The same test run a bit later with both header and data digests disabled:
Using 8000 Mb file:
And here is the same test with digests disabled:
Of course this is quick and dirty measurement, but at least now I have some baseline and tool to measure how changes in my infrastructure or its configuration influence performance. For example I saw interesting reports that NFS share on Synology outperform iSCSI target (at least in terms of IOps), and in other source there were graphs showing negligible performance cost of iSCSI digests (alongside these graphs that material emphasized importance of data integrity you gain with digests), but it will be nice to verify all these claims.
UPDATE (20.03.2015): I did the same tests with disabled digests (see additional screenshots above), so performance cost is not entirely negligible, especially for read and for large chunks of date.