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Server Administrator Storage Management 8.2 User’s Guide

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Virtual Disk Considerations For Controllers

In addition to the considerations described in this section, you should also be aware of the controller limitations described in Number of Physical Disks per Virtual Disk for the following controllers:
  • PERC 6/E and PERC 6/I
  • PERC H310 Adapter, PERC H310 Mini Monolithic, and PERC H310 Mini Blades
  • PERC H700, PERC H710 Adapter, PERC H710 Mini Blades, PERC H710 Mini Monolithic
  • PERC H800, PERC H810 Adapter
  • PERC H330 Adapter, PERC H330 Mini Monolithic, PERC H330 Mini Blades, PERC H330 Embedded
  • PERC H730P Adapter, PERC H730P Mini Monolithic, PERC H730P Mini Blades, PERC H730P Slim
  • PERC H730 Adapter, PERC H730 Mini Monolithic, PERC H730 Mini Blades
  • PERC H830 Adapter
  • PERC FD33xD/FD33xS
  • NOTE: The order of the controllers displayed on Storage Management may differ with the order of the controllers displayed in the Human Interface (HII) and PERC Option ROM. The order of the controllers does not cause any limitation.
The following considerations apply when creating virtual disks:
  • Creating virtual disks on controllers — When you create a virtual disk, you specify which physical disks are to be included in the virtual disk. The virtual disk you create spans the specified physical disks. Depending on the size of the virtual disk, the virtual disk may not consume all of the space on the physical disks. Any leftover space on the physical disks cannot be used for a second virtual disk unless the physical disks are of equal size. In addition, when the physical disks are of equal size and you use the leftover space for a second virtual disk, this new virtual disk cannot expand to include any physical disks not included in the original virtual disk.
  • Space allocation when deleting and creating virtual disks on controllers — When you delete a virtual disk, you free up or make available space on the physical disks that was being used by the deleted virtual disk. If you have created several virtual disks on a disk group, then deleting virtual disks can result in pockets of free space residing in various locations on the physical disks. When you create a new virtual disk, the controller must decide which free space on the physical disks to allocate to the new virtual disk. The PERC controllers look for the largest area of free space and allocate this space to the new virtual disk.
  • SCSI limitation of 2TB — Virtual disks created on a PERC controller cannot be created from physical disks with an aggregate size greater than 2TB. This is a limitation of the controller implementation. For example, you cannot select more than 30 physical disks that are 73GB in size, regardless of the size of the resulting virtual disk. When attempting to select more than 30 disks of this size, a pop-up message is displayed indicating that the 2TB limit has been reached, and that you should select a smaller number of physical disks. The 2TB limit is an industry-wide SCSI limitation.
  • Expanding virtual disks — You can only use the Reconfigure task to expand a virtual disk that uses the full capacity of its member physical disks.
  • Reconfiguring virtual disks — The Reconfigure task is not available when you have more than one virtual disk using the same set of physical disks. You can, however, reconfigure a virtual disk that is the only virtual disk residing on a set of physical disks.
  • Virtual disk names not stored on controller — The names of the virtual disks that you create are not stored on the controller. If you reboot using a different operating system, the new operating system may rename the virtual disk using its own naming conventions.
  • Creating and deleting virtual disks on cluster-enabled controllers — There are particular considerations for creating or deleting a virtual disk from a cluster-enabled controller.
  • Implementing channel redundancy — A virtual disk is channel-redundant when it maintains redundant data on more than one channel. If one of the channels fails, data is not lost because redundant data resides on another channel.
  • Rebuilding data — An failed physical disk that is used by both redundant and nonredundant virtual disks cannot be rebuilt. Rebuilding a failed physical disk in this situation requires deleting the nonredundant virtual disk.
  • Disk group concept consideration for S110 — Disk grouping is a logical grouping of disks attached to a RAID controller on which one or more virtual disks are created, such that all virtual disks in the disk group use all of the physical disks in the disk group. The current implementation supports the blocking of mixed disk groups during the creation of logical devices.

Physical disks are bound to disk groups, therefore, there is no RAID level mixing on one disk group.

Storage Management Server implements the disk group concept during virtual disk creation. Functionally, after a group of physical disks is used to create their first virtual disk, unused space in the disk is used only to expand the virtual disk, or create new virtual disks in the unused space. The virtual disks have identical RAID level.

Also, existing mixed configuration is not affected. However, you cannot create mixed configurations.

You can read or write to the virtual disks, rebuild, and delete the disks.

You cannot create virtual disks on a set of disks migrated from earlier software RAID versions and configured with multiple RAID levels.

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