I'm interested in the idea of sharing a bunch of SAS JBOD devices between two CentOS servers in an active-standby HA cluster sort of arrangement, and found something about using scsi3 persistent reservations as a fencing method. I'm not finding a lot of specifics about how this works, or how you configure two initiator systems on a SAS chain. I don't have any suitable hardware for running any tests or evaluations yet. general idea: 2 centos servers each with 8 port external SAS cards (2 x4), cascaded through a SAS box-o-disks with a whole bunch of SAS dual ported drives, to implement high availability large nearline storage. all storage configured as JBOD, using linux md raid or lvm mirroring. drives should only be accessible by the currently active server, with heartbeat managing the fencing. here's a hardware block diagram http://freescruz.com/shared-sas.jpg This is about the only details I've found on scsi persistant reservations and linux HA http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Configuration_Example_-_Fence_Devices/SCSI_Configuration.html One question I have is: how well will this scale with several strings of 100 SAS drives on the same HA pair of servers? Can SAS storage instead be fenced at the SES/expander level rather than having to use reservations with each separate drive? -- john r pierce N 37, W 123 santa cruz ca mid-left coast
