reg:// Cache policy

[sandilyan]

Hi all,

Please help me !!!!!!!!!!

I have doubt in what is cache policy in EVA ?

Thanks
Sandilyan S

[Víctor Cespón]

You mean on a vdisk?

You have read cache (ON / OFF)
And Write cache (Write-back / Write-through)

This is so you can choose to not perform any read or write cache on a vdisk. There may be some particular cases where that's needed, but usually both are enabled for performance reasons.

[sandilyan]

Hi ,

yes, i am tell about Vdisk in EVA .

can u help.

what is difference between Write-back cache & Write-through cache ?


Thanks
Sandilyan S

[Víctor Cespón]

Write-back means the data is stored on the EVA controller RAM and some time later writted on the disks.

Write-through means that the data is not stored on the cache and is written to the disks directly. This makes the operation appear slower to the server, since the RAM cache is not used.

The write cache in an EVA is battery-backed RAM, and a copy is stored on each controller, to have the security that even is there's a power or controller failure, data is not lost.

[sreekanthtm]

Hi,

Write back -- When a write request comes, EVA will write the data to the cache memory and aknowledge the Server. EVA will write this data to the diks later. This will increase the storage performance.

Wrire through -- EVA will not use the cache battery. Writing directly to the disk. this will take more time to aknowledge the write operation to the server (low performance).

Rgds,
Sreekanth.

[sandilyan]

Hi ,

Thank for u help me !!!!!!!!!!!


What is a quorum disk ?

what is the use of the quorum disk ?



Thanks
Sandilyan S

[Uwe Zessin]

Are you learning for a test? An end-user need not care about the EVA's quorum disks which are used to store meta-data.

[sreekanthtm]

Hi,

Quorum disk is used to store System-level metadata, like..
a. Controller information
b. World-Wide Name (WWN) and storage system name
c. Character map of disk groups and virtual disk members

There will be atleast one quorum disk per disk group.

Rgds,
Sreekanth.