Mixing 4210xs and 4210x

I have one 4210xs and one 4210x in the same group and a volume spanned across these two. How does it work with the SSD on the xs, is it used as cache for the 4210x also or is it only used for data that happens to be on the xs?

Responses(1)

A

Anonymous

5 Practitioner

•

274.2K Posts

1

February 3rd, 2016 08:00

Hello,

Sorry I missed this posting.

The SSDs can only affect storage on that specific member. It doesn't cache data from another member. That's the simple answer.

However, what really happens underneath is much more complicated than that. Short version, when multiple members are in the same pool, volume data is striped between them. It's done in proportion to their relative storage sizes. So if one member is twice the size of the other, 2/3 of the volume data will be on the larger member. The Capacity Load Balancer (CLB), tries to keep the free space balanced between them. So large writes to one, will get moved to the other. The other very important balancer is the Advanced Performance Balancer (APLB). If the two members are running at very different loads. (AKA latency) The less busy member will be given active blocks in exchange for idle blocks. This helps prevent "hot spot members".

Here are two Tech Reports that talk about the different balancers that Dell PS series storage uses.

The one for the Hybrid Array is here:

http://en.community.dell.com/techcenter/storage/w/wiki/4505.tr1092-equallogic-hybrid-array-load-balancer

The one for the standard balancer is here. That covers ALL models including the Hybrid.

http://media.community.dell.com/en/dtc/attach/tr1070%20-%20equallogic%20ps%20series%20architecture%20-%20load%20balancers.pdf

This one is a bit more of a marketing piece but I found it very useful as well.

https://marketing.dell.com/Global/FileLib/ANZ_DEF/03INFORM_2EqualLogic_Load_Balancers.pdf

Finally, there are many YouTube(tm) videos available.

https://www.youtube.com/watch?v=MNh2XLImbmE

Hopes this helps!

Regards,

Don