Symstat IO/sec vs Requests/sec

Hi guys,
I posted last week with a symstat/WP query that was sorted out in short order so now I'm back with another

What I'm doing is working my way through chapter 2 of a doc called 'EMC ControlCenter Performance Manager : The Symmetrix In Pictures' which is a cracking good document & I have a question around monitoring IO's vs Requests.

Just to be difficult I don't currently have access to ECC in my environment so what I'm doing is trying to translate the metrics discussed in the above document into SYMCLI/symstat commands that report the relevant info.

This question is around data alignment/IO's vs Requests.

The document says that the number of IO/sec coming from an FA should match pretty closely the number of Cache Requests/sec, hence indicating that the IO's are aligned on the cache slot boundaries.

Here's an edited symstat from our system showing 157 IO/sec for FA8B the number of cache requests is 10 read + 166 write.
The second line shows 23 IO/sec for FA8C with 1 read + 23 write cache requests/sec.

# symstat -sid 252 -type requests -dir all -i 5
DIRECTOR IO/sec Cache Requests/sec % RW
17:05:11 READ WRITE RW Hits
FA-8B 157 10 166 176 100
FA-8C 23 1 23 24 100

Can I assume from this very small subset of samples that the IO's are pretty much aligned & therefore not a problem ?


Now, given that my Sym is performing fine, I'm not worried about that currently, but want to make sure I know what unaligned IO looks like if I ever do see it so I've tried to mock up the output below........

Am I on the right sort of track here ? The document mentions that unaligned IO may use more than one cache slot & force a read to calculate CRC.

IE 157 IO/sec for FA8B would have reserved 416 cache slots which is way more than one per IO. The document notes that if you see requests reported as double the IO count then this can indicate unaligned IO.

# symstat -sid 252 -type requests -dir all -i 5
DIRECTOR IO/sec Cache Requests/sec % RW
17:05:11 READ WRITE RW Hits
FA-8B 157 250 166 416 100
FA-8C 23 23 23 46 100


If you guys could double check my logic &/or suggest any better symstat command for zeroing in on this type IO/sec vs Cache Requests/Sec info I'd really appreciate it.

Of course if anyone wants to ignore the question & poke fun at me for thinking about this kind of geeky stuff on a perfectly good Saturday when I should be doing normal things then that's fine too I have done some normal stuff too but seem to have slipped into Geek mode over the last hour :-p
Many thanks