Volumes; Utilizing Dm Storage Elements - HP 345646-001 - StorageWorks NAS 2000s External Storage Server Administration Manual

Storage Management Overview

Volumes

When planning dynamic disks and volumes there is a limit to the amount of growth a single
volume can undergo. Volumes are limited in size and are limited to no more than 32 separate
LUNs with each LUN not exceeding 2 terabytes (TB). Volumes also cannot exceed 64 TB of
disk space.
The RAID level of the LUNs included in a volume must be considered. All of the units that
make up a volume should have the same high-availability characteristics. In other words, the
units should all be of the same RAID level. For example, it would be a bad practice to include
both a RAID 1+0 and a RAID 5 array in the same volume set. By keeping all the units the
same, the entire volume retains the same performance and high-availability characteristics,
making managing and maintaining the volume much easier. It should be noted that if a
dynamic disk goes offline, then the entire volume dependent on the one or more dynamic disks
is unavailable. There could be a potential for data loss depending on the nature of the failed
LUN.
Volumes are created out of the dynamic disks and can be expanded on the fly to extend over
multiple dynamic disks if they are spanned volumes. However, once a type of volume is
selected it cannot be altered. For example, a spanning volume cannot be altered to a mirrored
volume without deleting and recreating the volume, unless it is a simple volume. Simple
volumes can be mirrored or converted to spanned volumes. Fault tolerant disks cannot be
extended either. Therefore, selection of the volume type is important. Please note that the same
performance characteristics on numbers of reads and writes apply when using fault tolerant
configurations as is the case with controller based RAID. These volumes can also be assigned
drive letters or be mounted as mount points off existing drive letters. In general, HP
recommends utilizing the Array controller for the management of fault tolerance over the use
of DM since DM places an additional level of operating system overhead on volumes. If
mount points are utilized, it should be noted that Services for Unix does not support mount
points at this time.
The administrator should carefully consider how the volumes will be carved up and what
groups or applications will be using them. For example, putting several storage-intensive
applications or groups into the same dynamic disk set would not be efficient. These
applications or groups would be better served by being divided up into separate dynamic disks,
which could then grow as their space requirements increased, within the allowable growth
limits.

Utilizing DM Storage Elements

No matter which type of storage element is created in DM the last step in creating the element
is determining its drive letter or mount point and formatting the element. Each element created
can exists as a drive letter(s), assuming one is available and/or as mount points off of an
existing folder of a drive letter. Either method is supported. However, mount points can not be
utilized for shares that will be shared using Microsoft Services for Unix (NFS). They can be
setup with both but the use of the mount point in conjunction with NFS shares causes
instability with the NFS shares.
Formats consist of NTFS, FAT32, and FAT and all three types can be used on the NAS device.
However, the Volume Shadow Copy Service can only utilize volumes that are NTFS
formatted. Also, quota management is possible only on NTFS.
54 NAS 2000s Administration Guide