Raid Tiering?

Dear All,

how does RAID Tiering work, especially in SC 2000 series? Is data moved between different RAID levels? Is it really physically moved or is there any abstraction layer? Is there any other name for this technique?

Somewhere I found a powerpoint presentation that suggests that data was held simultaneously in RAID level 10 for write and level 5 or 6 for read access. Is this possible? Is there any caching technique? When is determined what "hot" data is?

Is tiering reasonable when there are SAS disks only, no SSDs (or SATA as lower level)?

Thank you in advance.

- Chris

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RE: Raid Tiering?

Hello Chris,
The way that storage Tiers work is that all data is first put on to Tier 1 storage.  Now while this is going on in the background the SCOS is looking at all blocks of data and see which blocks are being access the most & which blocks of data are not being accessed very little.  After about 14-21 days the blocks that are not being access as much are moved from tier storage 1 to tier storage 2. Once that is done then on Tier 2 storage will look at all blocks and see which ones are getting accessed more often than the rest and will move the block that are not getting accessed to Tier 3 storage after about 14-21 days.

Data is moved between different raid levels as in all Tiers you can be running a mix of R10, R5-5, & R5-9.  If you are running Tiers with single redundant setup then the raid breakdown is as follows: R10=50%, R5-5= 20%, & R5-9=12%.  

If you are using a Dual Redundant setup then the raid types are a little different as you have R10, R6-6, & R6-10.  If you are running Tiers with Dual redundant setup then the raid breakdown is as follows: R10 Dual Mirror= 66%, R6-6= 33%, R6-10= 20%.

Also the data can be in multiple different raid types at the same time as the raid Tier is looking at the block level.  Any data that is being access regulary everyday will always stay on Teir1 storage.
Since you have all the same disk then if you were to use Tier storage then you would have Tier 1 & 3 storage.  The reason is that with all the same drive speeds then you have active data on Tier 1 and cold/ archive storage on Tier 3 storage.  

Here is also some other information about Tier storage:

Benefits of Tiering Storage
•    Maximize the usage of fast (expensive) disks for all volumes
•    Maximize the usage of all disks in the system
•    Spreading I/O to many disks is a primary advantage of virtualization
•    Minimize the overall system cost by needing less high speed disk
•    Data Progression moves infrequently accessed data to the slowest (cheapest) disks in the system

Tiering Facilitates Effective Management

Tiering supports the effective management of data storage:
•    Tiering allows you to group classes of storage
•    The ability to group classes storage allows the software to optimize cost and performance by enabling volumes to use recommended profiles
•    Cost and performance are optimized when volumes can be managed to use recommended profiles
•    Automate data movement to the proper storage class can be based on real-time usage
•    Minimize data management administrative time

RAID Devices and Storage Tiers

It is helpful to understand how RAID devices reside and function within Storage Tiers:
•    Raid devices live in every tier.  
•    The software (storage profiles) determine raid device usage and placement within tiers  
•    You can have different redundancy in different tiers but not in the same tier.
•    Each tier is considered to have it own disks.  
•    If one tier is full, the SAN will look for fastest available space to write to.
Please let us know if you have any other questions.

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