The following registry entries are associated with the SIOS DataKeeper service or driver and can be viewed and edited using Regedt32.

Registry Entries that MAY be Modified

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters

The SIOS DataKeeper driver uses the Parameters key and those below it. The values within the Parameters key (denoted with *) are global for all volumes on the system. The values under each of the Target IP registry keys (denoted with †) are specific to a mirror only. Values denoted with both * and † appear under both keys. (The target-specific value overrides the global value in this case.)

BandwidthThrottle †

Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\Volumes\{Volume GUID}\Targets\{Target IP}\BandwidthThrottle
Name Type Default Data
BandwidthThrottle REG_DWORD 0
Specifies the maximum amount of network bandwidth (in kilobits per second) that a particular mirror is allowed to use. A value of 0 means unlimited.

BitmapBaseDir *

*Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\BitmapBaseDir *
Name Type Default Data
BitmapBaseDir REG_SZ C:\%EXTMIRRBASE%\Bitmaps (usually C:\Program Files\SIOS\DataKeeper\Bitmaps but may be different when upgrading a system or if you install SIOS DataKeeper to a different path)
Specifies a directory where SIOS DataKeeper stores its Intent Log files. (Note: The drive letter must be in uppercase.) To disable the intent log feature, clear this registry entry (set it to an empty string) on all current and potential mirror endpoint servers. Disabling the intent log requires a reboot on each of these systems in order for this setting to take effect.

BitmapBytesPerBlock * †

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: If editing this entry under Parameters, all NEW mirrors created will inherit this value. If editing this entry under a {Target IP}, the value pertains to that one Target only. {Target IP} values override Parameter values.

Name Type Default Data
BitmapBytesPerBlock REG_DWORD 65536 (0×10000)

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.

BlockWritesOnLimitReached * †

Locations:

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

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

Note: If editing this entry under Parameters, all NEW mirrors created will inherit this value. If editing this entry under a {Target IP}, the value pertains to that target only. Any {Target IP} values override the global Parameter values.

Name Type Default Data
BlockWritesOnLimitReached REG_DWORD 0

This value determines what the behavior of a mirror is when the mirror’s Write Queue reaches a defined limit (WriteQueueHighWater or WriteQueueByteLimit reached). If BlockWritesOnLimitReached is “0”, the mirror is paused and a partial resync starts a short time later. If BlockWritesOnLimitReached is “1”, the incoming write is delayed until there is space on the write queue for it. The mirror remains in the Mirroring state, but the application throughput slows down to match the speed of the network and the remote node’s volume. After updating this registry value, execute the READREGISTRY command so that DataKeeper immediately starts using the new value.

Compression Level †

Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\Volumes\{Volume GUID}\Targets\{Target IP}\CompressionLevel
Name Type Default Data
CompressionLevel REG_DWORD 0
Specifies the compression level for the given mirror. Valid values are 0 to 9. Level 0 is “no compression”. Values from 1 to 9 specify increasingly CPU-intensive levels of compression. Compression level 1 is a “fast” compression – it does not require as much CPU time to compress the data, but results in larger (less compressed) network packets. Level 9 is the maximum amount of compression – it results in the smallest network packets but requires the most CPU time. The level can be set to somewhere in between, to balance CPU usage and network efficiency based on your system, network and workload.

DontFlushAsyncQueue *

Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\DontFlushAsyncQueue
Name Type Default Data
DontFlushAsyncQueue REG_SZ empty <drive letter>> [<drive letter>]
Allows the user to specify a volume or volumes that should not flush their async queues when the driver receives a flush request. This value should contain the drive letter(s) of the volume(s) to which this applies. Drive letters may be adjacent to each other (i.e. XY), or space separated (i.e. X Y), with no colons. After updating this registry value, execute the READREGISTRY command so that DataKeeper immediately starts using the new value. (Note: When setting DontFlushAsyncQueue, data and database logs should be on the same partition.)

MaxResyncPasses *

Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\MaxResyncPasses
Name Type Default Data
MaxResyncPasses REG_DWORD 200 (0xc8)

Specifies the maximum number of resync passes before SIOS DataKeeper temporarily interrupts the resync process while there is constant write activity on the source volume. Resync will be automatically resumed after this interruption, typically after 60 seconds. 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.

NotificationIconUpdateStatus *

Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\NotificationIconUpdateStatus
Name Type Default Data
NotificationIconUpdateStatus REG_SZ true
Allows the user to turn off status update checks performed by all instances of the DataKeeper Notification Icon on a machine. This value should contain either true or false. Disabling the Notification Icon via its context menu will set this entry to false.

PingInterval *

Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\PingInterval
Name Type Default Data
PingInterval REG_DWORD 3000 (0xBB8)
Specifies the interval in milliseconds between pings. Use a higher value for Wide Area Networks (WANs) or unreliable networks. Along with the MaxPingMisses, you may customize them to adjust mirroring to the network performance.

ResyncBlockWritesTimeoutMs *†

Locations:

For New Mirrors:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\ResyncBlockWritesTimeoutMs

AND

For Existing Mirrors:

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

Note: If editing this entry under Parameters, all NEW mirrors created will inherit this value. If editing this entry under {Target IP}, the value pertains to that target only. Any {Target IP} values override the global Parameter values.

Name Type Default Data
ResyncBlockWritesTimeoutMs REG_DWORD 150 (0×96)

Specifies the maximum amount of time that DataKeeper will delay writes during resync. See the Extensive Write Considerations topic for more information.

ResyncLowWater *†

Locations:

For New Mirrors:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\ResyncLowWater

AND

For Existing Mirrors:

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

Note: If editing this entry under Parameters, all NEW mirrors created will inherit this value. If editing this entry under {Target IP}, the value pertains to that target only. Any {Target IP} values override the global Parameter values.

Name Type Default Data
ResyncLowWater REG_DWORD 150 (0×96)

Specifies the maximum number of dirty blocks that can remain during resync before DataKeeper delays writes to allow the resync to complete. See the Extensive Write Considerations topic for more information.

ResyncReads *

Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\Volumes\{Volume GUID}\Targets\{Target IP}\ResyncReads
Name Type Default Data
ResyncReads REG_DWORD 20 (0×14)

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.

SnapshotLocation †

Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\Volumes\{Volume GUID}\SnapshotLocation
Name Type Default Data
SnapshotLocation REG_SZ <drive letter>
Specifies the folder where the target snapshot file for this volume will be stored.

TargetDispatchPort *

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\Targets{Target IP} (i.e. create a key whose name is the IP Address of the target system, or update the TargetDispatchPort value in that key if it already exists.)

Name Type Default Data
TargetDispatchPort REG_DWORD 9999

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\Targets\{Target IP} key if the mirror already exists. Create that key if it does not already exist. 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.

TargetPortBase *

Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\TargetPortBase
Name Type Default Data
TargetPortBase REG_DWORD 10000

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

TargetPortIncr *

Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\TargetPortIncr
Name Type Default Data
TargetPortIncr REG_DWORD 256

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.

TargetSnapshotBlocksize *

Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\Volumes\{Volume GUID}\TargetSnapshotBlocksize
Name Type Default Data
TargetSnapshotBlocksize REG_DWORD None

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.

VssQuiesceWaitTimeoutMs *

Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\VssQuiesceWaitTimeoutMs
Name Type Default Data
VssQuiesceWaitTimeoutMs REG_DWORD 60000
Specifies the amount of time (in milliseconds) the DataKeeper service will wait for a VSS Snapshot Source Initiate request to complete. The VSS Snapshot Source Initiate request uses VSS to quiesce the data on snapshotted volumes.

WriteQueueByteLimitMB †

Location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ExtMirr\Parameters\Volumes\{Volume GUID}\Targets\{Target IP}\WriteQueueByteLimitMB
Name Type Default Data
WriteQueueByteLimitMB REG_DWORD 0

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.

WriteQueueHighWater * †

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: If editing this entry under Parameters, all NEW mirrors created will inherit this value. If editing this entry under Target, the value pertains to that one Target only. Any Target values override Parameter values.

Name Type Default Data
WriteQueueHighWater REG_DWORD 20000 (0×4e20)

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.

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