(Richard Jones, TechTarget) Last year, at several seminars on advanced enterprise virtualization, I asked attendees about their virtualization deployments. Most had deployed VMware with the Virtual Machine File System (VMFS) as the storage file system, but few had deployed virtual machines (VMs) with raw device mapping (RDM) for storage access.

When creating storage for a VM, VMware's cluster file system, VMFS, is the default and follows the simple path, creating virtual disks inside a VMFS logical volume on a logical unit number (LUN). Then when you install a Linux OS, you can use the default. While the simple default settings for creating VMs may speed deployment and appear to reduce management overhead, these default settings pose problems. The central issue is that these settings target the simplest case without regard for particular system requirements. Defaults are often designed for a product evaluation, where ease and speed are the objectives. But particularly when it comes to disaster recovery (DR) and backup, consider the possible long-term effects of these default settings. Let's consider some enterprise scenarios to illustrate how default settings can be a bad move in virtual deployments.

Serverless backup and raw disk maps
As more modern applications are stored, it takes more time to back up or restore an application's data. But this opposes business disaster recovery demands of shorter recovery time objectives (RTOs). Compounding the situation is the ability of modern servers with more processor cores and memory to host higher VM consolidation ratios that can tax limited host backup/restore I/O bandwidth. All three factors have resulted in backup and recovery times that are unacceptable today compared with just a few years ago.

The solution is to move the backup and restore process away from VMs and to a storage area network (SAN) with serverless backup products such as VMware Consolidated Backup (VCB). Serverless backup requires RDMs to SAN LUNs to allow the backup server direct access to the LUN. But if a VM was created with defaults, you must re-create virtual disks and move data into RDM-configured storage to support a serverless backup architecture. This necessitates a major departure from default configurations for virtual environments.