Today we had an interesting discussion on the VCDX mailing list. One thing I noticed a while back when I was randomly looking around in “esxtop” was a new field. The field is called ” RESVSTATS and can be enabled in all disk related displays(d, u,v).
This will make troubleshooting storage related performance issues a bit easier as the SCSI Reservations(RESV/S) are shown a column(click the screenshot for a larger version) when enabled, and even more specifically SCSI Reservation Conflicts (CONS) are shown next to it):
Tomi Hakala says
There is similar counters also for VAAI (, go to disk devices statistics “u”, press “f” and toggle VAAI stats by pressing “o”. ATS is counter for atomic writes which are used instead of SCSI reservations on VAAI enabled systems.
Jason Boche says
Thanks for the heads up. I’m not seeing this discussion on the VCDX mailing list. Was this on an VMware internal list?
Jason Boche says
ESX 4.1: I see the metric in the D and U views, but not the VM specific V view:
Current Field order: aBCDEFgh
A: ID = Vscsi Id
* B: GID = Grp Id
* C: VMNAME = VM Name
* D: VSCSINAME = Vscsi Name
* E: NUM = Num of Vscsis
* F: IOSTATS = I/O Stats
G: LATSTATS/rd = Read Latency Stats (ms)
H: LATSTATS/wr = Write Latency Stats (ms)
Toggle fields with a-h, any other key to return:
Marco says
How much SCSI reservations would be problematic (for most environments) or is does this depend on the storage type / environment?
Morten says
Note that the CONS/s column that is added along with RESV/s shows SCSI Reservations conflicts! Also very useful. This was also shown at the ESXTOP session at VMworld.
Marco: i wouldn’t say that reservations are problematic, reservation conflicts are though, so this is what you should look for.
Adam Baum says
Is this only on ESX4.1? I don’t see it in 4.0 – tried d,u,and v and looked at all the available fields.
Duncan Epping says
Thanks Morten, just updated my post accordingly. Wasn’t able to watch the esxtop session yet. is definitely on my todo list.
udas says
Thanks for the helpful post.
Is this a typo?
In “the SCSI Reservations(RESV/S) are shown a column(click the screenshot for a larger version) when enabled, and even more specifically SCSI Reservations (CONS) are shown next to it):”
should the “SCSI Reservations (CONS)” not be “SCSI Reservation Conflicts (CONS)” ?
Mattias Sundling says
Does anyone know if these metrics will be available in vCenter in the future?
It makes monitoring much easier if you don´t have to connect to each ESX(i) host to gather this data.