On Fri, Jul 5, 2013 at 7:00 AM, Dennis Jenkins wrpte
No. iSCSI traffic between the VMWare hosts and the SAN uses completely separate NICs and different switches to the "production" LAN.
I've had a look at the task activity in VCEnter and found these two events
at almost the same time as the kernel messages. In both cases the start time (the first time below) is 5-6 seconds after the kernel message, and I've seen that the clock on the Postgres VM and the VCenter server, at least, are in sync (it may not, of course, be the VCenter server's clock that these logs get the time from).
I suspect that when a snapshot is deleted that all iSCSI activity either halts or slows SIGNIFICANTLY. This depends on your NAS.
I've seen an Oracle 7320 ZFS Storage appliance, misconfigured to use RAID-Z2 (raid6) to store terabytes of essentially random-access data pause for minutes when deleting a snapshot containing a few dozen gigabytes. (the snapshot deletion kernel threads get IO priority over "nfsd" file IO). This causes enough latency to VMWare (over NFS), that VMWare gave up on the IO and returned a generic SCSI error to the guests. Linux guests will semi-panic and remount their file-systems read-only. FreeBSD will just freak out, panic and reboot. The flaw here was using the wrong raid type (since replaced with triple-parity raid-10 and is working great).
