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TimeFinder from EMC

EMC has three instant copy products, TimeFinder/Mirror, TimeFinder/Clone and TimeFinder/Snap

The key differences between the products are summarised in the table below.

TimeFinder/Mirror TimeFinder/Clone TimeFinder/Snap

Copy

methodology

Full mirror. The mirror is always in

synch. with the source until the split

command is issued.

Point in time copy based on pointers

until copy process is complete

Point in time copy always based

on pointers

Copy space

requiredFull disk Full disk

Partial space depending on

amount of data updates.

Typically 30% of source

Availability of

copy data

BCV cannot be split off until the copy

process is complete

Copy is available as soon as the PiT

pointers are established

Copy is available as soon as the

PiT pointers are established

Performance

impactHardly any

Initial copy is a background process.

Some performance impact if data is

updated while copy is in progress

All initial updates will require

extra processing to move data.

DR capability Full DR once copy is completeFull DR once copy is complete, but not

if Copyonaccess setting is enabled

Minimal DR as full disk is

reliant on pointers to original

disk

Accessability of

copy

Not accessible until copy is complete

and the BCV is split from the

standard volume

Immediately accessible Immediate

Protection The BCV cannot be RAID5 The clone copy can be RAID5 The snap copy can be RAID5

All products can be managed by the EMC Replication Manager, if used for Open Systems data. Also, allproducts can use Copy Assist, a product which ensures a consistent Point-in-time copy over multiple disks,by temporarily freezing IOs until the copy is complete.

TimeFinder/Mirror

TimeFinder/Mirror uses dynamic mirror volumes called Business Continuity Volumes, or BCVs. TheTimeFinder terminology is Standard Volume (SV) for the primary disk, and BCV for the copy disk(s). A BCVis a mirrored copy of an SV, and has its own host address. You can have up to 16 copies, 4 of which can beactively copying data in the background. A BCV cannot be accessed while it is in association with a standardvolume, but if it is split from the SV, then it can be accessed for backup, testing or whatever.

The TimeFinder/Mirror Commands are -

To set up a BVC you must first create a device group, add an SV to it, then associate a BCV device to theSV. The BCV must be offline, and effectively becomes another mirror to the SV, so the BCV data is

synchronised with the Standard Volume. The commands below create a default type group called group1, add

a Standard Volume 01f to it, associate BCV device 110 to it, then starts to create the BCV data. As this is the

first time the BCV has been created, then a full establish is required.

symdg create group group1symld -g group1 add dev 01fsymbcv -g group1 associate dev 110symbcv -g group1 -full establish 01f bcv 110

To remove an association between the SV and the BCV you issue the split command. The point-in-time ofthe copy is the time the Split is issued. The SV is unaffected by a split. TimeFinder keeps a record of changed

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tracks after a split, to speed up a refresh of the BCV. The command below will split off a BCV once the copy

operation is complete.

symmmir -g group1 split

The establish command is used to re-synchronise a BCV which was formerly established, then split. It copiesover tracks which have been changed on the Standard Volume, and also replaces tracks which were changed

on the BCV with tracks from the SV, to get the BCV synchronised again.

symmmir -g group1 establish

It is also possible to restore the SV from data on a split BCV. This will restore the Standard Volume back tothe state it was in at the start of the Split command, provided the BCV has not been updated. The first

command just does a restore of changed tracks, the second command does a full restore of all the tracks.

symmmir -g group1 restoresymmmir -g group1 -full restore

If you want to report on the status of your BCV devices, use the following commands.

symmmir -g group1 query

For TimeFinder/Mirror, the point-in-time happens when the mirror split command is issued.

Timefinder/Snap

Timefinder/snap works by creating a new image of a LUN that consists of pointers that reference the data on

the original LUN. If any updates are scheduled to the source, the original data is copied to the snap beforethe source is overwritten. However, the snap does not reserve space for a full disk to cater for any updates.You allocate a 'Save Device', which is a common pool for original data which needs to be copied if updatesare made to the primary.Unlike other implementations, TimeFinder/Snap is designed for applications that need temporary access toproduction data, maybe for reporting or testing. It is not designed to be, nor is it suitable for disasterrecovery, as it is completely dependent on the existence of the source data.

The Snap utility can normally create up to 16 independent copies of a LUN, when the target data appears tobe frozen at the time that each Snap command was issued. You can increase this to 128 copies by issuingthe command

SET SYMCLI_MULTI_VIRTUAL_SNAPSIZE=ENABLED

The starting point for defining a snap copy is to set up a volume group that contains all the data that you wantsnapped. The examples below refer to a volume group called SNAPDB. Once you have your volume group,

you need to start the session between a standard volume and a snap copy with a create command. The device

numbers are for illustration only. Use your own device numbers. addall means add all the ungrouped devices

in the specified range, -vdev means the command just applies to virtual devices

symdg create SNAPB

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symld -g SNAPDB addall -range 00:09symld -g SNAPDB addall dev -range 3E:37 -vdevsymsnap -g SNAPDB create

Activate starts the copy-on-write process that preserves the snap copy.

symsnap -g SNAPDB activate -consistent

If you want to 'refresh' your snap copy to make it look like a current copy of the source group, you need toterminate the existing session, then re-establish the snap. This starts a new point in time copy using a

differential update.

symsnap -g SNAPDB terminate symsnap -g SNAPDB createsymsnap -g SNAPDB activate -consistent

RESTORE used to recover a volume back to the point in time state. This can be the original volume or a newvolume.

symsnap -g SNAPDB restore

Timefinder/Clone

TimeFinder/Clone volumes are called clone copies, and can be BCVs. The Clone copies can be in RAID5format and do not require that a previous mirror has been established . You can have up to 8 concurrentclone copies. Clone data is immediately accessable from a host, unlike standard BCVs where you need towait for the copy to complete.

TimeFinder/Clone has two activate modes; -copy and -nocopy. With the -copy mode you will eventually havea complete copy of the original disk at the clone, as it was at the point-in-time the activate command wasissued. With the -nocopy mode, only updated tracks are copied and uncopied data is maintained at theclone with pointers. Either option requires that the clone be the same size as the source. In open systems,Nocopy is the default and as all the data is not copied, it cannot be used as a DR position. The createcommand has a -precopy option that starts the full copy process off before the activate, so speeding up theprocess of creating a full copy. In a mainframe setup, the SNAP command automatically starts a full copyprocess.

The TimeFinder/Clone Commands are -

Create initiates a session between a standard volume and a clone copy. You can initiate sessions for an entiredevice group, between two devices in a group, or between two ungrouped devices. The first command below

assumes a device group called CLONEDB has already been defined and creates clone sessions to target

devices within the group. The second command will initiate a session between 2 specific devices. The thirdcommand uses the -precopy option so the copy process begins as soon as the clone relationship is established,

and -differential, which allows the clone to be refreshed at at later date.

symclone -g CLONEDB -tgt createsymclone create DEV001 sym ld DEV002symclone create DEV001 sym ld DEV002 -precopy -differential

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Activate makes the clone available for read/write and with the -copy option, starts the data copy process fromstandard volume to clone. The default action is no-copy, which means that only updated trackes are copied

over from the source. You can query the status of a clone, including the status of the copy process, with the

third command below. The copy status will be either 'copyinprog' or 'copied'.

symclone -g CLONEDB -tgt activate -consistent

symclone activate DEV001 sym ld DEV002symclone -g CLONEDB query

If the clone was started with the -differential option, it is possible to refresh the clone copy to the currentpoint in time. To do this you need to issue the recreate then activate commands below.

symclone -g CLONEDB -tgt recreate symclone -g CLONEDB -tgt activate -consistent

You use RESTORE to recover a volume or group back to the point in time state. This can be the originalvolume or a new volume. You need the -force option if your source volume is in an active RDF session with

remote R2 devices. The symclone query command will show the status as 'Restore in Progress' or 'Restored'.

Once the restore completes you need to split the clone before you can re-establish cloning in the normaldirection

symclone -g CLONEDB -tgt restore -forcesymclone restore DEV001 sym dev 0041symclone -g CLONEDB querysymclone -g CLONEDB split

Use terminate to break a clone relationship into discrete volumes, but the clone must be in 'copied' status orthe data on it will not be complete

symclone -g CLONEDB querysymclone -g CLONEDB terminate DEV001 sym ld DEV002