If one Googles “VMware storage issues”, the hit list is long and the links fairly recent. As users have rushed to embrace server virtualization, they have ended up placing demands on storage that put many storage vendors on the defensive. Indeed, at a recent VMWORLD conference there were several sessions on storage issues. And at another recent conference users complained that VMware is not friendly to N_Port ID virtualization (NPIV), a new approach that ties virtual HBAs directly to individual guest hosts.
But, the first consideration must be certification. Many disk array products and/or configurations have not yet been certified by the virtualization software vendor.
Second, there is performance. For virtual server environments, storage performance is truly king. Indeed, many users claim VMWare performance is fundamentally based on storage. Done right, the ability to scale both server and storage resources as needed is a tremendous benefit
Next is storage virtualization. As layers of virtualization are added, measurement tools have a more difficult time providing accurate performance and capacity measurements, making capacity planning and tuning difficult. Also, remember that not all applications can be virtualized, and some will require specialized storage for performance and other business imperatives (e.g. fax servers and heavy-hitting Citrix boxes).
Equally important is disk storage availability. A failure in a RAID group could end up impacting hundreds of servers. Thus vendors need RAID-6 or better and clever ways to manage the impact of rebuilds.
Traditional backups don’t work either, so disk-to-disk is mandatory and the snapshot copy capabilities must be robust and highly scalable and manageable. Even those using VMware’s own virtual machine file system (VMFS) say they enjoy less-than-ideal results, getting advanced features like file-level restore at the expense of placing a storage agent on each guest host.
Another requirement is virtual clones that allow a user to keep just one copy of a system image on disk and serve it up on multiple LUNs. Of course, booting over the storage network has to be bullet proof. And the storage has to understand that virtual servers can move dynamically and be able to shift things around in synch.
Then thin provisioning's many benefits create temptations. However, in this highly dynamic environment it is also important that the storage be provisioned and reallocated after use with the same simplicity as the virtual servers. A good commentary on this can be found at Thin provisioning: Look before you leap.
For convenience and cost, products offering multiple host interfaces are ideal. The list includes Fibre Channel, iSCSI, SAS, NFS and CIFS.
Finally, the biggest dangers generally are the result of configuration issues. When one starts to virtualize and abstract resources, it is very easy to end up with resources put together that don’t belong together. Thus users need to consider cross-domain reporting and monitoring tools, such as Akorri’s BalancePoint and Onaro’s SANScreen (now owned by NetApp) to improve troubleshooting, tuning and change management.
Not only does the storage industry need to meet all these requirements. It must also develop and market specialized software for environments like Oracle and SQL – e.g. snap manager for Oracle – and make this a margin opportunity. Better techniques that provide consistency across volumes are also badly needed.
Action Item: The storage industry must recognize the impact of server virtualization on storage requirements and embrace a new way of doing things that reflects the needs of virtualized environments --- and do it quickly!