ETERNUS DX Advanced Copy Functions

Transcription

1 ETERNUS DX Advanced Copy Functions 0

2 Content Equivalent Copy (EC) Session in General Equivalent Copy (EC) Concept EC Concept Diagram EC Cancel, Suspend and Resume Equivalent Copy - Process Mirroring Mechanisms in Comparison EC Equivalency EC Suspend and Resume in Detail EC Restore EC Summary 1

3 Equivalent Copy (EC) Session in General All Advanced Copy (AC) functions are executed in two separate phases After invoking the EC command First phase "Logical Copy" A bitmap that represents the on-going copy status is created in the ETERNUS CM cache Typically it takes a second or less to complete this process "Command completed" notification is returned Second phase "Physical Copy" The data of the source area is physically copied to the copy destination area The bitmap keeps a track of the copied (and not copied) data blocks Once copying is completed the bitmap in the ETERNUS CM cache is no longer used Until the EC session is suspended 2

4 Equivalent Copy (EC) Concept EC implements high speed (synchronous) copying of data between two Volumes From to Provides "mirror-on-demand" functionality for any Volume within an ETERNUS DX system As long the EC session is active the is locked The synchronization process must be completed before the equivalence of the mirror is available All data blocks of the Source must be copied to the Destination Now the EC process can be suspended (to be later resumed) During the "suspend" state the of the EC replication pair is again normally read and write accessible Note, the EC process is still running Suspend only temporarily interrupts the session Modifications on the Source and the are tracked in a bitmap 3

5 EC Concept Diagram EC must reach the equivalent state before can be detached Access to Source EC starts Logical copy done Write Equivalent State Write EC detach: suspend or cancel I/O request Source Volume Internal operation Logical copy Synchronize Physical copy EC complete Write data to both Two independent volumes Destination Volume troduction to Access to Destination ETERNUS SF Express Destination disk can not be accessed until stop/suspend I/O request 4

6 EC Cancel, Suspend and Resume (1) Cancelling EC terminates the session and a complete remirroring will be required when a new EC session is started All blocks need to be copied Only the changes made during the suspended state are copied when the session is resumed Changes to both - the Source and s - are recorded in a bitmap during the suspended state S D Cancel EC S D Write to Source or Start EC Re-mirroring Copy all data Equivalency state S D Resume Equivalency state Suspend EC Changes to Source and s are recorded in the bitmap when suspended Using the bitmap information, copy data only! or overwrite data only! 5

7 EC Cancel, Suspend and Resume (2) Suspend/Resume are functions to shorten the time for re-mirroring This reduces the time it takes to reach equivalent state after detaching the volumes Copy Rate Start /Cancel /Re-start EC Copy Rate Copy Phase Mirror Phase 0% 0% Start Copy Phase /Suspend /Resume EC Mirror Phase Short time Time Time Split Point Split Point 6

8 Equivalent Copy - Process (1) EC starts Replication proceeds in the background Block level copy from the copy source to the destination Copy rate depends on ETERNUS priority setting (High, Medium or Low) These parameters have to be assigned via the ETERNUS Mngr GUI or CLI The remains available The is inaccessible (locked) Access performance to source is degraded during active replication When replication is completed The mirror is kept synchronized / equivalent Detach request (cancel or suspend) Ensure data consistency before detaching an EC session Make sure applications running on are in backup mode Or otherwise consistent Or use the ACM pre- and post-script mechanism Both mirror Volumes are available for read and write access 7

9 Equivalent Copy - Process (2) Concurrent Suspend function This allows consistent copies of multi-volume data objects, such as databases All involved EC replication pairs have to be grouped together Can only be issued after all involved EC sessions have reached the Equivalent state Multiple EC sessions can be "suspended" at the same time point 8

10 Mirroring Mechanisms Comparison RAID-1 Uses mirroring for data redundancy Doubling the number of physical hard disks Ensuring that all data is physically duplicated on another physical disk This means that even if one disk fails, the data will still be available on the other disk Software mirroring Uses software running under the Operating System Protects against data lost due to physical disk failure by writing the data to two physically separated disks Disks are seen from the Operating System point of view, independent of the real physical disk type (local / remote or physical disks / RAID Volumes) Equivalent Copy (EC) Quick and easy copying of data by duplicating it in another RAID based logical disk (Volume) The participating Volumes can have any RAID level 9

11 EC Equivalency (1) When an EC command is issued Equivalency is established after complete mirroring A suspend/resume can be done after equivalency is established Host view Destination Volume Before EC starts Host view

12 EC Equivalency (2) The is created in the ETERNUS cache and the copy process is started All bits in the are set to "1" Host view Shows what has been copied to Destination Volume "1" means not copied yet

13 EC Equivalency (3) 1 st data block is copied from the to the Host view Is updated when section of data has been copied "0" means has been copied

14 EC Equivalency (4) 2 nd data block is copied from the to the Host view Is updated when section of data has been copied "0" means has been copied

15 EC Equivalency (5) 3 rd data block is copied from the to the Host view Is updated when section of data has been copied "0" means has been copied

16 EC Equivalency (6) 4 th data block is copied from the to the Host view Is updated when section of data has been copied "0" means has been copied

17 EC Equivalency (7) What happens when an application writes data to the Source Volume while the EC physical copy is going on? Host view 2 nd write 2 nd write Is checked first Since this section of data has already been copied to the, writing data to both Volumes can take place st check Application Data 16

18 EC Equivalency (8) Physical data block copying continues with the next block from to the. That is here the 5 th one Host view Is updated when section of data has been copied "0" means has been copied

19 EC Equivalency (9) 6 th data block is copied from the to the Host view Is updated when section of data has been copied "0" means has been copied

20 EC Equivalency () What happens with application write data to a data block that is not copied at all while the EC physical copy is going on? Host view 2 nd write 2 nd write Is checked first Since this section of data has not been copied to the, it is not synchronized yet So writing data to both Volumes can take place st check Application Data 19

21 EC Equivalency (11) Physical data block copying continues with the remaining not copied blocks from to the Host view Is updated when section of data has been copied "0" means has been copied

22 EC Equivalency (12) Last data block is copied from the to the Host view Is updated when section of data has been copied "0" means has been copied

23 EC Equivalency (13) EC has completed the initial copy process The Volumes remain Equivalent because every write operation in the source is duplicated in the destination Host view Shows that the physical copy is complete The status will show 0% (synchronized) EC Session Finished but still active 22

24 EC Suspend and Resume in Detail (1) The Volumes remain Equivalent until a suspend (break of the mirror) is invoked EC session can not be suspended before the Destination Volume is both logically and physically copied Equivalency has to be established first 23

25 EC Suspend and Resume in Detail (2) The continues to be updated during suspend Here new data is written in the now accessible New data is also written in the The bitmap is updated for all changes done in either Volume 01 0 Application Data Application Data 24

26 EC Suspend and Resume in Detail (3) When a resume is invoked the indicates which data blocks have changed and need consequently be copied to the to regain equivalency All changed data blocks in the are overwritten The is maintained during the resume process to show the current copy status

27 EC Restore After a cancelation the OPC mechanism can be used to restore the modified contents with the contents of the After a suspend a source restoration is possible by reversing the EC session The copy direction must be changed first with the task "reverse direction" The session has to be restarted with the task "resume" At the end the copy direction should be reverted back to original S EC suspended D S EC cancelled Restore with OPC D D EC reverse direction S D EC resume S 26

28 EC Summary EC is usable even if the Copy Source or Copy Destination Logical Volume is being formatted Copy Destination must have (at least) the same capacity as the Copy Source EC between encrypted volumes and unencrypted volumes is not possible When copying encrypted volumes the transfer performance is slightly degraded as compared to copying unencrypted volumes If power is turned off or fails during an active EC session the session will continue automatically from the point of interrupt as power is restored Cascading the s of an EC session have model specific restrictions Use the SA/SE Handbook as reference 27

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