IBM SG24-5360-00 ユーザーズマニュアル
1.2 VSE/ESA Support for the RVA
The RVA has been supported by VSE/ESA since its introduction. Because the
RVA presents itself as logical 3380 or 3390 direct access storage devices (DASD)
attached to a logical 3990 Model 3 storage control, releases of VSE/ESA
supporting this logical environment have functioned with the RVA. However,
until now, VSE/ESA has not provided SnapShot, deleted data space release
(DDSR) or capacity reporting natively. It has depended on VM/ESA
RVA presents itself as logical 3380 or 3390 direct access storage devices (DASD)
attached to a logical 3990 Model 3 storage control, releases of VSE/ESA
supporting this logical environment have functioned with the RVA. However,
until now, VSE/ESA has not provided SnapShot, deleted data space release
(DDSR) or capacity reporting natively. It has depended on VM/ESA
′
s IXFP and
SnapShot to provide that benefit to VSE/ESA guests.
1.2.1 What Is IXFP/SnapShot for VSE/ESA?
IXFP/SnapShot for VSE/ESA is a feature of VSE Central Functions in conjunction
with VSE/ESA Version 2, Release 3.1. It provides SnapShot, DDSR, and capacity
reporting support for the RVA. OS/390 and VM/ESA provide two distinct
products—IXFP and SnapShot—for supporting the RVA, whereas VSE/ESA has
integrated many of the functions provided by these products into a single feature
that implements the support in an Attention Routine command.
with VSE/ESA Version 2, Release 3.1. It provides SnapShot, DDSR, and capacity
reporting support for the RVA. OS/390 and VM/ESA provide two distinct
products—IXFP and SnapShot—for supporting the RVA, whereas VSE/ESA has
integrated many of the functions provided by these products into a single feature
that implements the support in an Attention Routine command.
1.2.2 What Is SnapShot?
SnapShot, one of the three functions in IXFP/SnapShot for VSE/ESA, enables you
to produce almost instantaneous copies of non-VSAM data sets, volumes, and
data within CYLINDER ranges.
to produce almost instantaneous copies of non-VSAM data sets, volumes, and
data within CYLINDER ranges.
Note:
Although not officially supported, VSAM data sets can be indirectly copied
through techniques we discuss in Appendix C, “VSE/VSAM Considerations” on
page 59.
page 59.
The speed in copying is attained by exploiting the RVA
′
s virtual disk architecture.
Snapshot produces copies without data movement. We call making a copy with
SnapShot a
SnapShot a
snap. The result of a SnapShot is also called a snap.
Conventional methods of copying data on DASD consist of making a physical
copy of the data on either DASD or tape. Host processors, channels, tape, and
DASD controllers are involved in these conventional copy processes. Copying
may take a long time, depending on available system resources.
copy of the data on either DASD or tape. Host processors, channels, tape, and
DASD controllers are involved in these conventional copy processes. Copying
may take a long time, depending on available system resources.
In the RVA
′
s virtual disk architecture, a functional device is represented by a
certain number of pointers in the FTD. Every used track has a pointer in the FTD
to its back-end data. You
to its back-end data. You
snap a copy of the data by copying its FTD pointers.
As you can imagine, snapping is a very fast process that takes seconds rather
than minutes or hours. No data movement takes place, and no additional
back-end physical space is used. Both FTD pointers, the original and the copy,
point to the same physical data location (see Figure 2 on page 4). Notice too
that the TNT entry now has a value of 2, which indicates that the data is in use
by two logical volumes.
than minutes or hours. No data movement takes place, and no additional
back-end physical space is used. Both FTD pointers, the original and the copy,
point to the same physical data location (see Figure 2 on page 4). Notice too
that the TNT entry now has a value of 2, which indicates that the data is in use
by two logical volumes.
Chapter 1. The IBM RAMAC Virtual Array
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