TPA nodes use vCenter/ESXi datastores to create pdisks used by Vantage. Datastores can be created from RAID-1 pairs, larger RAID 5/6 LUNs, or in other ways. Performance and redundancy are important criteria to be considered during storage configuration.
The following will help you determine the database size and help you calculate the Customer Data Space (CDS). CDS is the database space that is available for customer data.
- CDS Formula
- CDS = (Number of TPA vnodes * Number of pdisks per TPA vnode * pdiskSizeGB * sysinit and DIP * Compression) / Fallback
CDS = (Number of TPA vnodes * 3 * pdiskSizeGB * 0.7 * 2.5) / 2
- Sysinit and DIP (Database Initialization Program)
- The virtual Vantage system, sysinit, and the database supporting infrastructure take approximately 30% of raw pdisk space leaving approximately 70% for customer data.
CDS x Sysinit (30%) x Fallback (2) = Raw
- All virtual Vantage systems have Fallback turned on. Fallback divides available space by a factor of 2.Disabling Fallback can potentially result in data loss. Maintenance and support does not include resolution for problems that result from disabling Fallback. For more information, consult, go to https://support.teradata.com and search for KB0015393,Can FALLBACK be disabled?.
- All virtual Vantage systems have Compression turned on. A ratio of 2.5 is used for the compression calculation. Multiplying by 2.5 increases the available CDS.
- To determine the CDS, use the pdisk size as a starting point. The initial pdisk size is considered the raw disk size. You will set the size in the common.IT.properties.json file using the pdiskSizeGB property. Using the following formula: CDS x Sysinit x Fallback = Raw, PdiskdSizeGB = Raw / (number of vnodes x 3). Typically, the pdiskSizeGB property is set between 500 GB and 2 TB. Larger pdisk sizes reduce performance.
Use the CDS formula by entering the number of TPA vnodes and the virtual disk size to determine the total size of the virtual Vantage system.
Using the above formula, the following examples show how you can size according to the number of vnodes.
Assume a system comprised of 4 TPA virtual instances and a common properties pdiskSizeGB = 500 GB
CDS = (4 * 3 * 500 * 0.7 * 2.5) / 2 = 5250 GB
A CDS of 20 TB requires a pdiskSizeGB setting of 1536 GB which is equal to 1.5 TB. Use the CDS formula shown above to obtain the number of TPA vnodes.
Number of TPA vnodes = (CDS * 2) / (3 * pdiskSizeGB * 0.7 *2.5) *
Convert the CDS requested from TB to GB. For example, 20 TB = 1024*20 = 20480 GB. Next, add the numbers into the above formula.
For example: Number of TPA vnodes = (20480 GB * 2) / (3 * 1536 * 0.7 * 2.5) = 40960 / 8064 = 5.08 TPA vnodes
- CDS = (Number of TPA vnodes * 3 * pdiskSizeGB * 0.7 * 2.5) / 2
- CDS = (5.08 * 3 * 1536 * 0.7 * 2.5) / 2 = 20482 GB which translates to 20482 / 1024 = 20 TB
*2.5 is used for spool, fallback, and VMware overhead.