Registry Entries

Locations:

For New Mirrors: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\BitmapBytesPerBlock

For Existing Mirrors: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\Volumes\{Volume GUID}\Targets\{Target IP}\BitmapBytesPerBlock

Note:

Specifies the number of bytes that are represented as dirty in a DataKeeper Intent Log bitmap when a write request occurs. A single bit in the bitmap represents 65536 bytes, and the BitmapBytesPerBlock indicates the effective block size, which may be represented as multiple bits. Increasing this value can improve replication performance in some environments – in particular with workloads that perform sequential writes, on systems with relatively high-latency Bitmap storage. A larger block size means that fewer writes to the bitmap file will occur with sequential writes that are smaller than the adjusted block size. A larger block size will not noticeably help performance in environments where writes are primarily random, and may not help on systems with fast, low-latency bitmap storage. Also, a larger block size may result in larger amounts of data to resync in the event of a system failure.

Note: The minimum value of BitmapBytesPerBlock is 65536 – any value less than this is treated as 65536. There is no maximum value enforced.

Note: BitmapBytesPerBlock does not affect the rate of mirror resync.

Specifies the maximum number of resync passes before SIOS DataKeeper will give up trying to resynchronize the mirror while there is traffic on the source volume. In every pass, SIOS DataKeeper marks the volume blocks that were written to during the pass. In the next pass, it will send to the target only the marked blocks.

Note: In order for any changes to take effect a system reboot is required.

This value represents the maximum number of disk blocks that can be in the process of being read and sent to the target system during mirror resynchronization. Changing this value may change the speed of mirror resynchronizations.

Note: This tunable applies to synchronous and asynchronous mirrors.

Specifies the base TCP port number for target volume connections. This number may need to be adjusted if the default port is used by another service or is blocked by a firewall. The actual port that the target listens on is calculated as follows:

Port = TargetPortBase + (Volume Letter – A:)

For example:

TargetPortBase = 10000

Volume Letter = H

Port = 10000 + (H: -A:) = 10007

Specifies the increment to the base TCP port number. This is used only when a TCP port is found to be in use. For example, if the target is attempting to listen on port 10005 and that port is in use, it will retry listening on port 10005 + TargetPortIncr.

Locations:

On Target System:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\TargetDispatchPort

On Source System Creating Mirror to Above Target:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\TargetDispatchPort

AND

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\Volumes\{Volume GUID}\Targets\(Target IP}\TargetDispatchPort

There are two places where this should be set if you are changing the dispatch port from 9999. On the target system, place it in the ExtMirr\Parameters key. The new setting will apply to all existing and new targets on that server. A target reboot is required when the target Parameters key has been changed for this setting to take effect. On any source system that will be creating the mirror to this target, place it in the ExtMirr\Parameters key and also in the ExtMirr\Parameters\Targets\TargetIP key if the mirror already exists. Note: Make sure the ports are the SAME on both the source and the target.

A firewall port must also be opened manually on all source and target servers for the new dispatch port to work.

Specifies the maximum number of bytes that can be allocated for the write queue of this mirror (expressed in megabytes – multiples of 1048576 bytes). The value “0” means “no limit”. During periods of high disk write activity, if this mirror’s write queue grows to a level which reaches the WriteQueueByteLimitMB, the SIOS DataKeeper driver momentarily pauses the mirror, drains the queue and automatically starts a partial resync. After updating this registry value, execute the READREGISTRY command so that DataKeeper immediately starts using the new value.

This value is used during transmission of volume data to the target, when the mirror is in the Mirroring state as well as when the mirror is in the Resync state. You should ensure that the ResyncReads value (see below), which specifies the number of 64KB (65536 byte) blocks that can be put on the Write Queue during resync, does not exceed the limit specified by WriteQueueByteLimitMB. Multiply ResyncReads by 65536, then divide by 1048576 – the resulting value must not exceed WriteQueueByteLimitMB if WriteQueueByteLimitMB is not set to 0.

This value can be used in conjunction with WriteQueueHighWater (see below). If both limits are set to nonzero values, then the mirror will be paused if either of them is reached. If one is set to 0 and one is not, then the nonzero limit is the only one that is enforced. If both are set to 0, then the mirror’s write queue is not limited at all (this is not recommended – the WriteQueue uses Nonpaged memory).

Note: This tunable applies to synchronous and asynchronous mirrors. You can monitor the mirroring behavior using the SIOS DataKeeper Performance Monitor counters – specifically the Queue Current Bytes value – and set this limit accordingly.

Locations:

For New Mirrors:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\WriteQueueHighWater

AND

For Existing Mirrors:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\Volumes\{Volume GUID}\Targets\{Target IP}\WriteQueueHighWater

Note

Specifies the maximum number of write requests – not the number of bytes – that can be stored in this mirror’s write queue. The value “0” means “no limit”. During periods of high disk write activity, if this mirror’s write queue length reaches this value, the SIOS DataKeeper driver momentarily pauses the mirror, drains the queue and automatically starts a partial resync. After updating this registry value, execute the READREGISTRY command so that DataKeeper immediately starts using the new value.

This value is used during transmission of volume data to the target, when the mirror is in the Mirroring state as well as when the mirror is in the Resync state. You should ensure that the ResyncReads value (see below), which specifies the number of blocks that can be put on the Write Queue during resync, does not exceed the limit specified by WriteQueueHighWater if WriteQueueHighWater is not set to 0.

This value can be used in conjunction with WriteQueueByteLimitMB. If both limits are set to nonzero values, then the mirror will be paused if either of them is reached. If one is set to 0 and one is not, then the nonzero limit is the only one that is enforced. If both are set to 0, then the mirror’s write queue is not limited at all (this is not recommended – the WriteQueue uses Nonpaged memory).

Note: This tunable applies to synchronous and asynchronous mirrors. You can monitor the mirroring behavior using the SIOS DataKeeper Performance Monitor counters – specifically the Queue Current Length value – and set this limit accordingly.

Note: This setting has been replaced by ResyncReads and is no longer used.

Locations:

For New Mirrors:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\WriteQueueLowWater

AND

For Existing Mirrors:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\Volumes\{Volume GUID}\Targets\{Target IP}\WriteQueueLowWater

Note

DataKeeper target snapshot uses a default block size of 64KB for all entries that are written to the snapshot file. This block size can be modified by creating this TargetSnapshotBlocksize registry key.

The value should always be set to a multiple of the disk sector size, which is usually 512 bytes. Certain workloads and write patterns can benefit from changing the block size. For example, a volume that is written in a sequential stream of data (e.g. SQL Server log files) can benefit from a larger block size. A large block size results in fewer reads from the target volume when consecutive blocks are written. But a volume that is written in a random pattern may benefit from a smaller value or the default 64KB. A smaller block size will result in less snapshot file usage for random write requests.

Specifies a text string containing the version number of the last SIOS DataKeeper driver to have booted on this system.

Note: Any changes in the following values will take effect after the next system reboot.

Specifies a bitmap of the volume attributes set by the SIOS DataKeeper Service. Used internally by the service and the driver.

BIT 0: All Net Alert

BIT 2: Resync Done Alert

BIT 3: FailOver Alert

BIT 4: Net Failure Alert

BIT 5: LifeKeeper Configured

BIT 6: Auto Resync Disabled

Specifies the drive letter of the volume on the target side at the time of a mirror creation or continue. This value is the Unicode representation of the drive letter.

This value is written by the driver during a mirror creation or continue operation and is present for informational purposes only. The driver does not read this value.

Note: It is possible for drive letters to change while the system is running. This can be done by using the Disk Management utility and other methods. This value is only accurate as of the last mirror create or continuation.

WARNING: THIS VALUE SHOULD NOT BE CHANGED BY THE USER.

Specifies the drive letter of the volume on the source side at the time of a mirror creation or continue. This value is the Unicode representation of the drive letter.

This value is written by the driver during a mirror creation or continue operation and is present for informational purposes only. The driver does not read this value.

Note: It is possible for drive letters to change while the system is running. This can be done by using the Disk Management program and other methods. This value is only accurate as of the last mirror create or continuation.

WARNING: THIS VALUE SHOULD NOT BE CHANGED BY THE USER.

Indicates the current mirroring state of a volume.

WARNING: THIS VALUE SHOULD NOT BE CHANGED BY THE USER.

Indicates the type of mirroring this volume is engaged in.

WARNING: THIS VALUE SHOULD NOT BE CHANGED BY THE USER.

Determines whether the mirror was broken or paused because of an error or because the user requested the break/pause. If this entry indicates a break error, the system attempts to recover from the break/pause.

Note: This entry is used internally by the SIOS DataKeeper driver.