Tuesday, November 13, 2007

Caching






From the chart above, the amount of Cache that a Clariion contains is based on the model.

Read Caching
First, we will describe the process of when a host issues a request for data from the Clariion.

1.The host issues the request for data to the Storage Processor that owns the LUN. If that data is sitting in Cache on the Storage Processor,
2.The SP sends the data back to the host.

If however, the data is not in Cache, the Storage Processor must go to disk now to retrieve the data. (Step 1 ½ ). It reads the data from the LUN into Read Cache of the owning Storage Processor. (Step 1 ¾ ) before it sends the data to the host.

Write Caching

1.The host writes a block of data to the LUN’s owning Storage Processor.
2.The Storage Processor MIRRORs that data to the other Storage Processor.
3.The owning Storage Processor then sends the Acknowledgement back to the host, that the data is “on disk.”
4.At a later time, the data will be “flushed” from Cache on the SP out to the LUN.

Why does Write Cache MIRROR the data to the other Storage Processor before it sends the acknowledgement back to the host?

This is done to ensure that both Storage Processors have the data in Cache in the event of an SP failure. Let’s say that the owning Storage Processor crashed (again, never happens). If that data was not written to the other Storage Processor’s Cache, that data would be lost. But, because it was written to the other SP Cache, that Storage Processor can now write that data out to the LUN.

This MIRRORing of Write Cache is done through the CMI (Clariion Messaging Interface) Channel which lives on the Clariion.

2 comments:

Anonymous said...

29047126483369175 I play dofus Replica Watches for one year, I Replica Rolex Watches want to get some Replica Watch kamas to buy Replica Chanel Watches item for my character. So, I search "Replica Swiss Watches" on google and found many website. As Exact Replica Graham Watch the tips from the forum, I just review the Swiss Replica Watches websites and choose some Replica Montblanc Watches quality sites to Replica Cartier Watches compare the price, and go to their Replica Breguet Watches online support to make Replica Breitling Watches the test. And Last Chaos Gold I decide to use Replica BRM Watch at the end. And Tag Heuer Replica Watch that is the Replica IWC Watch beginning..

swiss replica watches said...

Georges Favre-Jacot at within 1929, by which inturn occasion Zenith possessed accomplished watch-making past earning esteemed cash incentives along with awards meant for time attempting to keep accuracy through global demonstrations throughout Geneva, Paris, france, Spain's funding, as clearly as Neuchatel. Across 1969, Pinnacle made much of our planet's initially computerized chronograph move, Swiss Replica Watches the El Primero. In addition to the this essential, the thing who makes this exact motion individual is going without shoes oscillating with Thirty five, 000 alternations each individual hour, and thus it definately will calculate short time durations to somewhat of a 10th of any second, a very good unparalleled society report on 1969. On 1998, Peak introduced a different technology replica MontBlanc watches relating best imitation Panerai watches to ultra-thin motion, the individual Professional, with been really lately specific as very finest physical movements considering Swiss Replica Watches UK the expert storage devices. Zenith was honored throughout 1, Five-hundred Best Replica Watches UK bucks incentives plus commendations -- making Zenith quite possibly the most granted Switzerland brand.