Windows supports up to 255 iSCSI LUNs maximum. This creates a hard limit on the number of VDBs that can be created because each VDB requires one or more iSCSI connections.
iSCSI connections - Staging
- dSource linked with Logsync disabled = 1 LUN (DATA)
- dSource linked with Logsync enabled = 2 LUNs (DATA and ARCHIVE)
- dSource linked with Logsync disabled and SnapShot started (new COPY ONLY FULL BACKUP) = 3 LUNs (DATA and TEMP)
- dSource linked with Logsync enabled and SnapShot started (new COPY ONLY FULL BACKUP) = 3 LUNs (DATA, ARCHIVE and TEMP)
- Once the SnapShot is completed the TEMP LUN will be destroyed and 2 LUNs used
- A maximum of ~120 dSources per Staging Target is recommended, assuming an average of 2 LUNs per source, which would mean 240 LUNS would be consumed for normal operation.
- The proposed scenario would leave 13 additional iSCSI connections available for COPY ONLY FULL BACKUPS
- For dedicated staging hosts, we do NOT use a Powershell process for monitoring.
iSCSI connections - Targets
- VDB normal operations = 1 LUN (DATA)
- No extra mounts required for SnapShot restore or refresh from source Snapsync
- VDB point-in-time log actions (such as restore, refresh or provision from logs) = 2 LUNS (DATA and SOURCE_ARCHIVE)
- An extra LUN is not required for Snapsync operations, only Logsync
- Most users do not require enablement of the Logsync feature for MSSQL Sources, because sources in FULL RECOVERY mode create a Snapsync for each log file, providing a significant number of restore points even without retaining the logs.
- Once recovery is completed the SOURCE_ARCHIVE LUN will be destroyed and 1 LUN used
A maximum of ~120 VDB's per Target is recommended
- In 4.x, target host iSCSI connections are less likely to be a limitation while processing costs for Powershell threads may become prohibitive because each target VDB requires a Powershell process for monitoring
- In 5.x, this has been alleviated with a hard limit on Powershell processes
iSCSI connections - V2P
- V2P normal operation = 1 LUN (DATA)
- Once the V2P operation is completed the DATA LUN will be destroyed leaving no LUNs used
- V2P point in time log actions (provision from logs) = 2 LUNS (DATA and SOURCE_ARCHIVE)
- Once the V2P operation is completed both the DATA and SOURCE_ARCHIVE LUNs will be destroyed leaving no LUNs used