The following table lists the advantages and disadvantages
of using the various types of copy blades for your System Level Backup
or offload method.
System Level Backup method
| System Level Backup Method |
Vendor |
Advantages |
Disadvantages |
| FlashCopy® |
IBM® (EMC,
HDS, or any vendor that supports FlashCopy emulation) |
With FlashCopy emulation, IMS can be across several vendors DASD. Technology to drive FlashCopy in IMS Recovery Expert is very fast. (Very small amount of time to issue
the FlashCopy commands) DFSMSdss can be used to drive
fast-replication data set restore of IMS object data sets.
Users can specify target ranges so there is no need to update a profile when IMS expands to new volumes. Does not require SMS. |
Log suspend required. Older EMC FlashCopy emulation (pre 72 microcode)
is somewhat slower. HDS FC emulation is quite slow also elongating
the log suspend time. Not an incremental copy - all tracks are copied
in the background on each backup. Fast database restore (through DFSMSdss)
will use host based IO (slow copy) if the background copy is not complete.
Volumes must be clipped and brought online to offload to tape. |
| TimeFinder Mirror (BCVs) |
EMC |
Uses EMC Consistency. No log suspend needed. Backup is completely
done and usable at split time. Restores can be done right away. Snap
data set can be used for almost instantaneous restore of IMS database data sets. Does not require SMS.
Fast database restore can be performed through Snap data set without
clipping and bringing the volumes online. |
Two phase backup. Establish BCV (wait for sync), then split
BCV to make backup. If you have N generations of
backup disks, you only get N-1 backups on disk
because one generation is always mirroring the source volumes. IMS must be completely on EMC DASD.
When IMS expands to new volumes,
profile must be updated to add new BCV target units. Volumes must
be clipped and brought online to offload to tape. |
| TimeFinder Clone (Full volume snap to target volume) |
EMC |
Uses EMC Consistency. No log suspend needed. Can be performed
in phases (phased snap) so performance implications to source volumes
can be timed and mitigated. Snap is differential; only changed tracks
are copied since the last backup. Snap data set can be used for almost
instantaneous restore of IMS database
data sets. Users can specify target ranges so there is no need to
update a profile when IMS expands
to new volumes. Does not require SMS. Fast database restore can be
performed through Snap data set without clipping and bringing the
volumes online. |
Full system restore must wait until background copy is complete.
Fast database restore (Snap data set) must wait until background copy
is also complete. IMS system
must be completely on EMC DASD. |
| TimeFinder Snap (Virtual Device Snap - VDEV) (V2.2) |
EMC |
Uses EMC Consistency. No log suspend. Space efficient snap. Does not need a full backup
volume for each source IMS volume. Many backup points can be
saved on fast-replication disk. Uses a "SAVE POOL" to store changes to source device after the
backup is taken. Users can specify target ranges so there is no need to update a profile when IMS expands to new volumes. Does not require SMS. |
Must monitor the save pool to ensure it does not fill up. Also,
a true disk backup never exists; only the changed tracks are stored
in the save pool. Cannot perform a Snap data set restore from this
type of backup. IMS system must
be completely on EMC DASD. |
Offload method
| Offload Method (Archive Method) |
Vendor |
Advantages |
Disadvantages |
| DFSMSdss |
IBM |
Can be used for any backup method. Users have finer control
over data set name used to hold the volume dump. All options to offload
each profile are contained in one product (no need to go to HSM to
configure dump classes). |
All DFSMSdss tasks are run in one address space, limiting the
number of simultaneous tape dumps you can run concurrently. If the
backup disks are offline, they need to be clipped and brought online
before they can be copied to tape. |
| Fast Dump and Restore (FDR) |
Innovation |
Can be used for any backup method. FDR generally considered
faster than DFSMSdss. Users have finer control over data set name
used to hold the volume dump. All options to offload each profile
are contained in one product (no need to go to HSM to configure dump
classes). |
All FDR tasks are run in one address space, limiting the number
of simultaneous tape dumps you can run concurrently. If the backup
disks are offline, they must be clipped and brought online before
they can be copied to tape. |
| FDR Instant |
Innovation |
Can be used for any backup method but real advantages come
when using in conjunction with a backup method that leaves target
units offline. FDR Instant eliminates the need to clip the target
unit and bring it online. It can copy the volume while it is offline. |
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