Vdisk RAM or permanent memory?

Database
Enthusiast

Vdisk RAM or permanent memory?

All AMPS are connected to their respective vdisk and and share nothing with other AMPS.

Theses vdisks are part of RAM/memory or permanant disk array storage that are attached to node ?

Document says each AMP acquire portion of database storage. so the cylinders that constitutes vdisks are part of RAM/memory of node or permananet storage? 

Its very confusing. Need Help.

2 REPLIES
Enthusiast

Re: Vdisk RAM or permanent memory?

Hi Shashank,

 

Vdisks are part of permanent storage i.e. Physical disk. In teradata Physical disk can be called as RAID array of disks where data is stored permanently.

 

Virtual Disks (vdisks)

The groups of pdisks assigned to an AMP are collectively identified as a vdisk. Vdisks are used to control the assignment of pdisks to AMPs.

Teradata Employee

Re: Vdisk RAM or permanent memory?

Teradata storage is virtualized at several levels. 

 

The storage for an AMP is allocated by the virtual storage system (TVS). One a unit of storage is allocated to an AMP, that AMP is the sole owner of that storage and no other AMP can access it in any way (thus shared nothing data). TVS can have several kinds of physical storage from which to allocate to an AMP. depending on the physical platform employed. For instance in a 6xxx platform there is likely spinning disk and solid state storage. TVS allocates a share of both the spinning disk and SSD to each AMP. All data in Teradata has a home location on some form of persistent storage. TVS also monitors the utilization of each cylinder of data and uses that information to optimize the location of each part of the data on the storage. More frequently used data will be moved to faster storage (eg SSD) and less frequently used data will be moved to the slowest portions of the spinning disks - all automatically and continuously.

 

Additionally, each AMP has two physical RAM memory allocations (Teradata Intelligent Memory (TIM) and FSGCache). These two spaces are used by the AMP to intelligently cache data from the persistent storage owned by that AMP. Again, these memory allocations are exclusive to the AMP, no other AMP will read or operate on data in the memory allocated. Data can be modified in this memory but the memory is not persistent so it is always a cache not the home location for the data. The TIM cache contains the most frequently used data, driven by the TVS statistics on usage. This very frequently used data is pinned in the cache. The FSG cache contains most recenty used data to provide a transient cache of data being used by applications at this time. Like the placement, the caching is all automatically and conntinuously operated by the system.