Measuring Disk Capacity And Volume Size; Block Systems And File Systems; Storing File System Data On A Block System - HP StoreVirtual 4000 User Manual

Table 46 Information on the System Use tab
Category
Name
Raw space
RAID configuration
Usable space
Provisioned space

Measuring disk capacity and volume size

All operating systems that are capable of connecting to the SAN via iSCSI interact with two disk
space accounting systems—the block system and the native file system (on Windows, this is usually
NTFS).
Table 47 Common native file systems
OS
Windows
Linux
Netware
Solaris
VMware

Block systems and file systems

Operating systems see hard drives (both directly connected [DAS] and iSCSI connected [SAN])
as abstractions known as "block devices": arbitrary arrays of storage space that can be read from
and written to as needed.
Files on disks are handled by a different abstraction: the file system. File systems are placed on
block devices. File systems are given authority over reads and writes to block devices.
iSCSI does not operate at the file system level of abstraction. Instead, it presents the iSCSI SAN
volume to an OS such as Microsoft Windows as a block device. Typically, then, a file system is
created on top of this block device so that it can be used for storage. In contrast, an Oracle
database can use an iSCSI SAN volume as a raw block device.

Storing file system data on a block system

The Windows file system treats the iSCSI block device as simply another hard drive. That is, the
block device is treated as an array of blocks which the file system can use for storing data. As the
iSCSI initiator passes writes from the file system, the SAN/iQ software simply writes those blocks
into the volume on the SAN. When you look at the CMC, the used space displayed is based on
how many physical blocks have been written for this volume.
When you delete a file, typically the file system updates the directory information which removes
that file. Then the file system notes that the blocks which that file previously occupied are now
freed. Subsequently, when you query the file system about how much free space is available, the
space occupied by the deleted files appears as part of the free space, since the file system knows
it can overwrite that space.
152 Provisioning storage
Description
Host name of the storage system.
Total amount of disk capacity on the storage system. Note:
Storage systems with greater capacity will only operate to
the capacity of the lowest capacity storage system in the
cluster.
RAID level configured on the storage system.
Space available for storage after RAID has been
configured.
Amount of space allocated for volumes and snapshots.
File System Names
NTFS, FAT
EXT2, EXT3
NWFS
UFS
VMFS