TPA nodes use vCenter/ESXi datastores to create pdisks used by Teradata Database. Datastores can be created from RAID-1 pairs, larger RAID 5/6 LUNs, or in other ways. When you choose how to design the underlying storage devices to create datastores, take performance into consideration.
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.
- 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. All Teradata Database vNodes have 3 pdisks so a single Teradata Database vNode has a raw total pdisk size of 3 * pdiskSizeGB. If pdiskSizeGB = 100, then 3 * 100 = 300 GBytes of raw pdisk on a single Teradata Database vNode. Typically, the pdiskSizeGB property is set between 500 GB and 2 TB. Larger pdisk sizes reduce performance.
- Sysinit and DIP (Database Initialization Program)
- The virtual Teradata Database system, sysinit, and the database supporting infrastructure take approximately 30% of raw pdisk space leaving approximately 70% for customer data.
- All virtual Teradata Database systems have Fallback turned on. Fallback divides available space by a factor of 2.Fallback should not be turned off. If your database goes down, Teradata Customer Support may not be able to assist in recovering your data.
- All virtual Teradata Database systems have Compression turned on. A ratio of 2.5 is used for the compression calculation. Multiplying by 2.5 increases the available CDS.
- CDS Formula
- CDS = (Number of Teradata Database TPA vNodes * Number of pdisks per TPA vNode * pdiskSizeGB * sysinit and DIP * Compression) / Fallback
CDS = (Number of Teradata Database TPA vNodes * 3 * pdiskSizeGB * 0.7 * 2.5) / 2
Use the following formula by entering the number of Teradata Database vNodes and the virtual disk size to determine the total size of the virtual Teradata Database 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 = 500GB
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 1.5TB. Use the CDS formula shown above to obtain the number of Teradata Database vNodes.
Number of Teradata Database 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 Teradata Database vNodes = (20480 GB * 2) / (3 * 1536 * 0.7 * 2.5) = 40960 / 8064 = 5.08 Teradata Database vNodes
- CDS = (Number of Teradata Database 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