Lets be very clear – the DACstore area of the disk drives in the DS4000 family is only 512MB. That’s it! A flat amount. It does not increase as the drive capacity increases, it is not a percentage of the total capacity of the drive. It is simply 512MB in total. The size of the DACstore on firmware level V7.10 remains at the same 512MB size.
For those of you wondering, the DACstore is a (512MB) reservation on the physical drives in a DS4000 subsystem that holds information about the DS4000 configuration. Here they are listed below (as found in the ‘IBM System Storage DS4000 and Storage Manager’ book pg134):
- Drive state and status
- WWN of the DS4000 controller (A or B) behind which the disk resides
- Logical drives contained on the disk
- Failed drive information
- Global Hot Spare state/status
- Storage subsystem identifier (SAI or SA Identifier)
- SAFE Premium Feature Identifier (SAFE ID)
- Storage subsystem password
- Media scan rate
- Cache configuration of the storage subsystem
- Storage user label
- MEL logs
- LUN mappings, host types, and so on.
- Copy of the controller NVSRAM
So, this information is stored on every physical drive in a DS4000 subsystem (including drives in any expansions) all in the 512MB space.
This lends to some inherent advantages that tend to be quite unique to the DS4000 family. For example, drives can be rearranged within the subsystem at a very low risk. What I find very fascinating is the ability for all DS4000 subsystems to recognise both configuration and data in drives from other DS4000s. That’s right, you guessed it … upgrades or migrations with data intact.
Now because I am paranoid when it comes to data, please consult your friendly IBM certified specialist before you play any advanced game of checkers with your drives.
1 Comment
May 15, 2009 at 6:17 pm
Thanks for the brief detail wyzzi, this is exactly what I was looking for..