Storage Changes in VMware ESX 3.5 Update 3

Just over three months after releasing Update 2 for ESX 3.5, VMware has released Update 3. That last Update brought major storage changes like VSS support, hot VMFS extension, Storage VMotion across Fibre Channel and iSCSI, and support for 10 Gb Ethernet and 8 Gb FC support.

For more information on Update 2, see my article, Storage Fixes in VMware ESX Server 3.5 Update 2.

Update 3 is not as important from a storage perspective, but there are some goodies in there:

• New VMDK recovery tool (nifty!)
• Storage tweaks like fixed multipathing on IBM SVC, interrupt coalescing on QLogic 4 Gb FC HBAs, and some bug fixes
• Expanded support for SATA (but not for VMFS), SAS, and some Broadcom NICs (but still no TOE)

Read on for more details!

VMDK Recovery Tool

ESX users with Update 3 get a nifty new script for deeper inspection of disk image files on VMFS. Although I haven’t had a chance to try it out yet, it appears to be related to VCB, in that it identifies which disk blocks make up a VMDK. But the VMDK Recovery script (which runs in Service Console on ESX – sorry, ESXi!) allows you to copy these blocks to a new file.

What good is this? Well, it could certainly be used to recover VMDK files from corrupted VMFS datastores, and could serve as an undelete feature as well. And as Rich Brambley points out on VM/ETC, it could be the basis for some nifty scripted backup and restore operations as well. I’m looking forward to seeing what happens with this, but it’s definitely a minor addition.

Storage Tweaks

Update 3 includes some minor tweaks and bug fixes in storage:

• ESX used to only support most-recently used (MRU) multipathing with IBM’s SAN Volume Controller storage virtualization platform, but Update 3 allows fixed policies to be used as well.
• The VMkernel iSCSI driver gets two new advanced configuration options (Disk.UseLunReset and Disk.UseDeviceReset) to control whether multipath failover will issue a LUN reset or target reset.
• SCSI sense codes are now included in /var/log/vmkernel by default.  This should assist in deep troubleshooting of storage problems.
• The lengthy iSCSI target discovery process that used to happen whenever a discovery address was added has been removed, speeding up iSCSI storage configuration.
• Users of QLogic 4 Gb Fibre Channel HBAs will now get updated firmware and a new performance feature called interrupt coalescing. As it sounds, IC will combine interrupts from multiple I/Os, improving overall performance by reducing the number of interrupts the CPU has to handle.

Note that VMware ESX 3.5 Update 3 still doesn’t really make maximal use of 10 Gb Ethernet. Besides the lack of TCP offload engine (TOE) support, the company still doesn’t make any speed claims when people step up to faster NICs. The Known Issues list specifically says it’s for connectivity, not performance. At least the QLogic iSCSI HBA support is pretty good.

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