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Symmetrix TimeFinder - Possible Questions for Interview

What is Business Continuity?

Business Continuity is the preparation for, response to, and recovery from an application outage that adversely affects business operations.

What are the Business Continuity tools available for symmetrix?

Power path at host end TimeFinder/Mirror, Clone and Snapshot for local replication SRDF for remote replication.

Business Continuity addresses what?

Business Continuity Solutions addresses systems unavailability, degraded application performance, or unacceptable recovery strategies.

What is RPO and RTO?

RPO refers to the maximum amount of data loss an application can tolerate as measured in time. In other words, the amount of data loss that can be tolerated (cost of transaction versus risk).

RTO refers to the maximum time a company budgets to bring an application back online in the event of a disaster. In other words, the time it takes to recover the data once a disaster or other recovery event is declared (risk versus cost)

What are the different types of Device Groups?

Regular, RDF1, RDF2 and Composite group

Briefly explain baout Regular, RDF1 and RDF2 device groups?

Regular device groups are normally used for TimeFinder operations
RDF1 and RDF2 device groups are normally used for SRDF operatins

What is composit group?

A composite group is a user-defined group of device members that can span multiple Symmetrix arrays and SRDF groups. The CG type may be defined as REGULAR,RDF1, RDF2, or RDF21, and may contain various device lists for standard, BCV, virtual (VDEV), RBCV, BRBCV, second hop standard, and second hop BCV.

What is the difference between TimeFinder and SRDF?

Time Finder is for local replication operations
SRDF is for remote replication operations

What is the purpose of TimeFinder/ Mirror, Clone and SNAP?

TimeFinder/Mirror : Backups and Web content refresh
TimeFinder/Clone : Data warehousing and Application testing
TimeFinder/Snap : Local recovery and 1-hour RPO

What are all possible commands used for TimeFinder Operations (Mirror, Clone and Snapshot)?

Symmir is for timefinder mirror operations
Symclone is for timefinder clone operations
Symsnap is for timefinder snap operations
symconfigure is for devices creation
symdg is fir device group operations
symld is for performing operatoins on devices in a device group
symbcv is for performing operations on devices in a device group
symdev is for performing operations on devices
symcfg is for performing configuratoin related operations

What is the BCV device?

BCV is Business Continuance Volume
Can be dynamically and non-disruptively established and synchronized
Can be split instantly to create “point-in-time” copy.
Uses for the BCV copies can include backup, restore, decision support, and applications testing.

Explain step by step procedure for TimeFinder Mirror Operations?

Establish: Synchronize the standard volume to the BCV volume
Split: Terminate mirror relationship between standard and BCV volumes
Restore: Synchronize contents of BCV volume to the standard volume
Verify: Provide current status of BCV/standard volume relationship.

Creating regular device group
symdg create -type regular

Adding standard devices to the device group
symld -g add dev -sid XXXX

Associating BCV devices to the device group
symbcv -g addl dev -sid XXXX

Establish mirror relationship between STD and BCV devices
symmir -g -full establish -v

Verifying the synchronization status
symmir -g verify -synched

Splitting mirror relationship between STD and BCV devices
symmir -g split

Restoring BCV
symmir -g restore

Verify the restore status
symmir -g verify -synched

What is the status of Source and Target devices at the time of Establish, Split and Restore in mirror operations?

Establish: STD device have R/W access and BCV device is in NR state.
Split : Both STD and BCV will have R/W access
Restore : STD device have R/W access and BCV device is in NR state.

How will synchronization happen when perform establish?

The Symmetrix array checks that both the standard device and the BCV device are the same size, the device specified as the BCV has the BCV attribute, the standard device does not already have a BCV device assigned to it.
If the standard device is a meta head device, then the BCV must also share the same meta device properties. All meta members will be implicitly established along with the meta head device.
The BCV device is set as Not Ready to the host.
The BCV device is assigned as the next available mirror of the standard device.
The contents of the standard device are copied to the BCV.

What is the background process in split operation?

Command validity is checked. For example, the Symmetrix array makes sure that the standard device has an active BCV mirror and that the standard and BCV devices comprise a BCV pair.
I/O is suspended to the standard device until the split operation completes.
Any pending write transactions to the standard device and the BCV device are destaged.
The BCV device is split from the BCV pair.
The BCV device state is changed to Ready, enabling host access through its separate address (BCV001).

What is default option while performing establish?

Incremental is the default action for establish.

What is Power path Split?

Power Path holds I/O during split - Read and write I/O, executed from host doing I/O, affects only one host, does not require independent access to a gatekeeper.

What is ECA (Enginuity Consistent Assist) split?

Symmetrix holds I/O during split - Write I/O (subsequent reads after first write), Executed by any Symmetrix-attached host, multiple host support, requires independent access to a gatekeeper.

What are the precautions we have to take while performing establish?

Host access to BCV devices must be stopped.
Stop application, unmount file system, and deactivate volume group.

What are the precautions we have to take while restoring a mirror?

All access to the STD device must be stopped. Applications must be stopped, file systems must be unmounted, and volume groups must be deactivated when a restore is initiated. Since the host is having read and write access to the standard device, if any application is using the standard volume during a restore, the results would be unpredictable.

What is Protected BCV Establish?

Both M1 and M2 of standard device instantly synchronized with the M1 and M2 of 2-way mirror BCV.
In a 2-way BCV mirror configuration for a normal establish M2 is fixed and can only be updated from M1 after a split.

What is reverse split?

Data will be moved from the M2 mirror of the BCV to its M1 mirror.
During a reverse split, the fixed BCV mirror (M2) will refresh the moving mirror (M1) after the split operation. This is desirable when we need to revert to an older copy of the data that was on the BCV before it was established.

What is Protected BCV Restore?

A protected restore feature allows the contents of a BCV to remain unchanged during and after a restore operation, even while the BCV and the standard are joined.
Restore a BCV to a STD but do not propagate STD writes to the BCV – Used to retain original BCV data after the restore process

How many BCVs can be supported in multi BCV functionality?

Eight BCVs

How many BCVs can be established concurrently to the standard volume?

Two BCVs

Is TimeFinder Mirror Supports concurrent restores?

Concurrent restores are not allowed.

Is the BCV can be mounted to the source host?

BCV mirror can be mounted to same host but there will duplicate disk signatures/volume IDs need to change.

One device can be a member of how many device groups?

Only one device group

Device Groups are host based or Array based?

Host based. If we enable the GNS in symmetrix array then we can create array wide device group.

What is foreground and background instant split?

Foreground split completes instantly and returns a success status to the production.
Background split continues to split the mirror until the split is complete. If the production server tries to access information on a track that has not been split,the system first splits the track and then completes the I/O request

Expbrlain Step by step procedure for TimeFinder Clone Operations?

Create: Create relationship between standard and Clone
Activate: Clone is now active and available immediately for read/write access – Production I/O is processed against standard
Re-Create: Clone is re-attached to Standard for new point-in-time copy (incremental/differential)
Establish: Create and activate
Restore: Re-attached to Standard and incremental or full restore is performed
Terminate: Terminate the relationship between source and target

symdg create -type regular
symld -g add -sid dev XXX1
symld -g add -sid dev XXX2
symclone -g create
symclone -g activate
symclone -g query
symclone -g terminate

What are the different options with clone create and Explain?

CopyOnAccess: Only modified tracks are copied to clone volume after activation
Full Device Copy: Full copy in the background starts after activation
Precopy: Full copy in the background starts after creation
Differential: Used with Full Copy or Precopy (implied Full Copy by default) – Required if recreate clone session is planned – Required if incremental restore is planned.

Can we use STDs as a target for Clone?

Yes, we can use standard or BCV as a clone.

How many CopyOnAccess sessionw symclone will support?

Up to 16 CopyOnAccess sessions

How many concurrent Full copied session clone will support?

Up to 4 concurrent Full Copied sessions

When we have to use –defferential option while create a clone session?

If clone recreate is planned or incremental restore is planned.

What will happen when we activate the clone session?

Places the target in the Read/Write (RW) state
Initiates copying if the -copy option has been specified in the symclone create command
Omitting the -copy option in the symclone create command defers data copying until either tracks on the source are written to or tracks on the target are read or written to

Explain Step by step procedure for TimeFinder Snap Operations?

symsnap –g savedb create DEV001 vdev ld VDEV005 –svp save_db

symsnap –g savedb activate DEV001 vdev ld VDEV005

symsnap restore DEV001 vdev ld VDEV005

symsnap –g savedb terminate DEV001 vdev ld VDEV005

How the copy session works in symsnap operation?

Once the Time Finder Snap session is activated:
When a host attempts to write to the data on the production volume, the original track is first copied to the “Save Area”, then the write is processed against the production volume. This process of pointers maintains the consistent, point-in-time copy of the data for the ongoing snapshot.

What is the background process while terminating the clone session?

When a copy session is terminated
The virtual device is made not ready
Tracks on the save device(s) are reclaimed if they are not referenced by any other copy session
The copy session structures are freed up

How many snapshots can be created from a single source volume?

Upto 15 snap sessions can be create with source volume.

How many snapshot can be created in multi virtual?


What will happen if save area is run out of space?

The target VDEV goes in Not Ready (NR) state, applications beware! Copy-on-write is disabled and the source track is changed.

What is the recommended size of VDEV?

1/600th the size of a source device

How the data will be stored in save devices in a save pool?

Data will be stored in a save pool as a round-robin manner.

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