Every once and awhile when using SOIC (Storage IO Control) within ESXi the hosts will get out of wack with regards to reading and writing to the slotsfile. If you take a look at your syslog output you might see something like the below.
<14>2013-12-12T06:49:58.987Z vmsrv-13.uwgb.edu storageRM: open /vmfs/volumes//VM-LUN-1/.naa.60002ac0000000000000002900001234/slotsfile(0x10000042, 0x0) failed: No such file or directory
<14>2013-12-12T06:49:58.987Z vmsrv-13.uwgb.edu storageRM:Giving UP No such file or directory Error -1 opening SLOT file /vmfs/volumes//VM-LUN-1/.naa.60002ac0000000000000002900001234/slotsfile
<14>2013-12-12T06:49:58.987Z vmsrv-13.uwgb.edu storageRM:Error -1 in opening & reading the slot file
<14>2013-12-12T06:49:58.987Z vmsrv-13.uwgb.edu storageRM:Failed to read slot file
The correction to this is pretty fortunately is very simple.
Lets stop the SOIC service
/etc/init.d/storageRM stop
Now lets start it
/etc/init.d/storageRM start
Monitor the syslog entries for the next few seconds and you should see them clear up pretty quickly.
Original reference for this post came from Frank over at . Same issue, just seeing in a different area of vSphere.