ng

US 2003/0131182 A1
address, a virtualiZation switch of this invention must ?rst
convert those instructions to a physical target address before
instructing the target.
[0048] Targets may be divided into physical or virtual
“logical units.” These are speci?c devices addressable
through the target. For example, a physical storage sub
system may be organiZed in a number of distinct logical
units. In this document, hosts vieW virtual memory as
distinct virtual logical units. Sometimes herein, logical units
Will be referred to as “LUNs.” In the SCSI standard, LUN
refers to a logical unit number. But in common parlance,
LUN also refers to the logical unit itself. Central to virtu
aliZation is the concept of a “virtualiZation model.” This is
the Way in Which physical storage provided on storage
subsystems (such as disk arrays) is related to a virtual
storage seen by hosts or other initiators on a netWork. While
the relationship may take many forms and be characteriZed
by various terms, a SCSI-based terminology Will be used, as
indicated above. Thus, the physical side of the storage area
netWork Will be described as a physical LUN. The host side,
in turn, sees one or more virtual LUNs, Which are virtual
representations of the physical LUNs.
[0049] The mapping of physical LUNs to virtual LUNs
may logically take place over one, tWo, or more levels. In the
end, there is a mapping function that can be used by sWitches
of this invention to interconvert betWeen physical LUN
addresses and virtual LUN addresses.
[0050] FIG. 2 is a block diagram illustrating an eXample
of a virtualiZation model that may be implemented Within a
storage area netWork in accordance With various embodi
ments of the invention. As shoWn, the physical storage of the
storage area netWork is made up of one or more physical
LUNs, shoWn here as physical disks 202. Each physical
LUN is a device that is capable of containing data stored in
one or more contiguous blocks Which are individually and
directly accessible. For instance, each block of memory
Within a physical LUN may be represented as a block 204,
Which may be referred to as a disk unit (DUnit).
[0051] Through a mapping function 206, it is possible to
convert physical LUN addresses associated With physical
LUNs 202 to virtual LUN addresses, and vice versa. More
speci?cally, as described above, the virtualiZation and there
fore the mapping function may take place over one or more
levels. For instance, as shoWn, at a ?rst virtualiZation level,
one or more virtual LUNs 208 each represents one or more
physical LUNs 202, or portions thereof. The physical LUNs
202 that together make up a single virtual LUN 208 need not
be contiguous. Similarly, the physical LUNs 202 that are
mapped to a virtual LUN 208 need not be located Within a
single target. Thus, through virtualiZation, virtual LUNs 208
may be created that represent physical memory located in
physically distinct targets, Which may be from different
vendors, and therefore may support different protocols and
types of traf?c.
[0052] Although the virtualiZation model may be imple
mented With a single level, a hierarchical arrangement of any
number of levels may be supported by various embodiments
of the present invention. For instance, as shoWn, a second
virtualiZation level Within the virtualiZation model of FIG.
2 is referred to as a high-level VLUN or volume 210.
Typically, the initiator device “sees” only VLUN 210 When
accessing data. In accordance With various embodiments of
Jul. 10, 2003
the invention, multiple VLUNs are “enclosed” Within a
virtual enclosure such that only the virtual enclosure may be
“seen” by the initiator. In other Words, the VLUNs enclosed
by the virtual enclosure are not visible to the initiator.
[0053] In this eXample, VLUN 210 is implemented as a
“logical” RAID array of virtual LUNs 208. Moreover, such
a virtualiZation level may be further implemented, such as
through the use of striping and/or mirroring. In addition, it
is important to note that it is unnecessary to specify the
number of virtualiZation levels to support the mapping
function 206. Rather, an arbitrary number of levels of
virtualiZation may be supported, for eXample, through a
recursive mapping function. For instance, various levels of
nodes may be built and maintained in a tree data structure,
linked list, or other suitable data structure that can be
traversed.
[0054] Each initiator may therefore access physical LUNs
via nodes located at any of the levels of the hierarchical
virtualiZation model. Nodes Within a given virtualiZation
level of the hierarchical model implemented Within a given
storage area netWork may be both visible to and accessible
to an alloWed set of initiators (not shoWn). HoWever, in
accordance With various embodiments of the invention,
these nodes are enclosed in a virtual enclosure, and are
therefore no longer visible to the alloWed set of initiators.
Nodes Within a particular virtualiZation level (e. g., VLUNs)
need to be created before functions (e.g., read, Write) may be
operated upon them. This may be accomplished, for
eXample, through a master boot record of a particular
initiator. In addition, various initiators may be assigned read
and/or Write privileges With respect to particular nodes (e. g.,
VLUNs) Within a particular virtualiZation level. In this
manner, a node Within a particular virtualiZation level may
be accessible by selected initiators.
[0055] As described above, various sWitches Within a
storage area netWork may be virtualiZation sWitches sup
porting virtualiZation functionality. FIG. 3A is a block
diagram illustrating an exemplary virtualiZation sWitch in
Which various embodiments of the present invention may be
implemented. As shoWn, data or messages are received by
an intelligent, virtualiZation port via a bi-directional con
nector 302. In addition, the virtualiZation port is adapted for
handling messages on behalf of a virtual enclosure port, as
Will be described in further detail beloW. In association With
the incoming port, Media Access Control (MAC) block 304
is provided, Which enables frames of various protocols such
as Ethernet or ?bre channel to be received. In addition, a
virtualiZation intercept sWitch 306 determines Whether an
address speci?ed in an incoming frame pertains to access of
a virtual storage location of a virtual storage unit represent
ing one or more physical storage locations on one or more
physical storage units of the storage area netWork. For
instance, the virtual storage unit may be a virtual storage unit
(e.g., VLUN) that is enclosed Within a virtual enclosure.
[0056] When the virtualiZation intercept sWitch 306 deter
mines that the address speci?ed in an incoming frame
pertains to access of a virtual storage location rather than a
physical storage location, the frame is processed by a
virtualiZation processor 308 capable of performing a map
ping function such as that described above. More particu
larly, the virtualiZation processor 308 obtains a virtual
physical mapping betWeen the one or more physical storage