EVA Cache related.

[Hasan_9]

Hello All,

What does write-back cache do in EVA controllers?
How does this cache work in each Slave and Master Controller?
How does it work in Active/Active and Active/Passive environment?
Is there any online doc in this regard?

Thx
Hasan

p.S. This thread has been moevd from Disk to Storage Area Networks (SAN) (Enterprise). - Hp forum Moderator

[Víctor Cespón]

Hi, let's take a EVA3000 for example. Each controller has 2 GB of RAM, 1 GB for controller data and 1 GB for cache.

The 1 GB cache is divided on 512 for read cache, 256 MB for own write cache and 256 MB for copy write cache.

Every time a write is sent to the EVA, it's stored on the write cache and copied though the mirror port to the other controller memory too (so in case a controller fails, the pending writes do not get lost)

The Active/Active firmware does not change this, you can access a LUN though all external ports, but all writes are cached on both controllers.

[Amar_Joshi]

Answers to your questions may differ a bit depending on your EVA (GL or XL).

What does write-back cache do in EVA controllers?
- WBCache store the pending write data temporarily and acknowledges to host that data has been written. This avoids the slow response to hosts and virtually makes the transaction done.


How does this cache work in each Slave and Master Controller?

- Write cache is mirrored to avoid any data lose in case one of the controller fails. Read cache in independent to perform optimal.


How does it work in Active/Active and Active/Passive environment?

- A/A or A/P keeps more sense to host connection. In A/A host see 2 controllers to write to and in A/P only one. A/A is good for multiple LUN distribution to balance the LUNs evenly across two controllers.

Is there any online doc in this regard?

- CommandView Usermanual some how talks about it but it's good if you can attend the EVA administration training by HP or borrow the manual from someone who did. Link for CV-EVA UG:
http://search.hp.com/redirect.html?type=REG&qt=command+view+eva+user+guide&url=http%3A//h20000.www2.hp.com/bc/docs/support/SupportManual/c01081029/c01081029.pdf%3Fjumpid%3Dreg_R1002_USEN&pos=2