Virtual machine drops ISCSI drives during Vmotion

celerra 1Recently during maintenance downtime early one Sunday morning, our VMware administrator was v-motioning numerous VM’s to patch the host environment blades on the Cisco UCS. One of the VM’s was a Windows 2008 R2 server that contained over 10 iSCSI connections to targets residing on an EMC Celerra NS-40G NAS. All migrations were going well until this particular VM was moved: all of the iSCSI drives disappeared from the Windows OS. A vMotion process is a transparent process and this should not have happened, but this time it had a negative effect on the VM: an unexpected glitch. This happens time to time. The iSCSI initiator in the Windows Server OS still registered the connections as connected and online, but the OS disk management would not see the drives.

celerra iSCSI targets

I disconnected and then re-connected the targets in the iSCSI client, but the Windows OS would still not see the drives. I restarted both the iSCSI initiator and Server service in the Windows OS with the same result. Re-scanning for storage in Windows disk management did not help. EMC tech support ran a check on the NAS end and came up with nothing. Eventually, I went into Celerra Manager and deleted the LUN masking for the target and then re-added it. The Windows Server OS was then able to see the drives. I was hesitant to do his at first, as I was unsure what effect it would have on the drive letter assignments on the server: it had no effect on that – all drives were reestablished as the previously were.

celerra iSCSI target LUN masking

EMC CLARiiON Cx4 integrated thin provisioning

virtualizationWe just upgraded to the new EMC CLARiiON Cx4 from the Cx3 over the weekend. The technician who arrived had done a good job: in about seven hours, the SAN was fully functional and we were back in business. We took this downtime to do some patching on host systems. The Cx4 has 8Gb fiber ports as compared to the Cx3 4Gb ports; however we could not use the 8Gb modules as the NAS, an EMC NS40g, contains code that is not 100% compatible with the Cx4 fiber module code. We will run it all on the 4Gb/s fiber modules for now until the NAS code catches up, and then the 8Gb modules will be installed. This is not a problem, as the 4Gb modules are still very fast and provide sufficient throughput for our electronic health records system (EHR).

One useful improvement about the Cx4 is the addition of thin pools – one can create RAID groups that use minimal storage and can expand dynamically when the need for more storage arises. See the white paper from EMC on virtual (thin) provisioning here.


virtualizationSome good links about virtualization from –

Storage Virtualization solves problems

virtualizationAccording to a 2005 article by Informationweek, EMC Kicks Off Storage-Virtualization System; Invista uses out-of-band communications and SAN switches to map logical addresses to physical addresses and improve the utilization of storage resources, virtualization enables the reconfiguring of storage without disabling applications as well as better storage utilization. Virtualization can simplify storage administration. Vendors such as EMC use out of band virtualization from the SAN switches, where IBM, with its SAN Volume Controller product use in-band in which virtualization mapping “takes place at devices residing in the data path… [and] “Virtualization allows the management of the IT infrastructure to be independent of the management of applications”” (Informationweek, 2005). Virtualization is the “ability to take storage and present it to any host, of any size, from any storage vendor” (Anthes, 2008). It also provides more efficient use of disk space and can streamline “operations by simplifying migration, replication, and backup” (Informationweek, 2009).

EMC Kicks Off Storage-Virtualization System; Invista uses out-of-band communications and SAN switches to map logical addresses to physical addresses and improve the utilization of storage resources. May 16, 2005 pNA InformationWeek, p.NA. Retrieved June 11, 2009

Anthes, G. (Oct 6, 2008). Virtual headaches: storage virtualization is hot and for good reason. But its benefits bring layers of complexity.(SPECIAL REPORT). Computerworld, 42, 41. p.24(4). Retrieved June 12, 2009, from Academic OneFile via Gale

HP Launches Virtualized Storage Hardware, Software; The StorageWorks offerings can reallocate and manage resources across virtual and physical environments, reducing costs by avoiding excess storage capacity.(Brief article). March 10, 2009 pNAInformationWeek, p.NA. Retrieved June 12, 2009, from Academic OneFile via Gale