quick msa1000 question - cache

[Mike Gentles]

I am pretty sure that the individual controllers mirror the cache between dimms when 2 are used.....but does it actively mirror the cache from one controller to the other when using redundant controllers???

The HSG family does when using 2 HSG80's in an MA8000 for example. But I can not see how it would with the MSA since there is no active/active config but rather still using active/standby.

TIA,

Mike Gentles

[Mike Naime]

Mike

The Maintenance and Service guide mentions a 128M Cache Module with Battery. It even shows how to replace the Cache Module and batteries.

The users guide indicates that Cache is split between read and write cache under Chapter6: CLI > Display Commands > Viewing Controller Settings. It makes no mention of mirrored Cache.

Mike

[Doug de Werd]

In a redundant configuration, the MSA's RAID controllers absolutely mirror the cache (write cache, not read) across the controllers. This is a key element for having redundant controllers and maintaining optimum performance.

Even though the controllers are active/passive in terms of servicing I/O requests, the passive controller is still receiving and caching all of the write requests going to the first controller. This way, if the first controller fails, the second one picks up exactly where it left off and continues to write I/O's to the disk, even if they are queued up in cache.

The mirrored cache is stated in the "msa controller" section of the specs at http://h18006.www1.hp.com/products/quickspecs/11033_div/11033_div.html

Thanks,
Doug