Will vSAN use both cahe tier while using FTT=1 Raid1

[baber]

When we create vmB with FTT=1 Raid1 so it has 2 replica from each object for example 2vmdk disk that one of them has resided on host1 and the other resided on host2 1- The cache data for vmB on the both hosts (host1 and host2) is same ?

2- want to know when we want to read a data it will be read from cahce of both hosts or will use just cahche of one server ?

[depping]

No the data stores on the caching device isn't necessarily the same. vSAN will periodically evict blocks from cache to capacity, depending on various aspects, but one being the capacity used of the caching tier. Depending on the size of the cluster, how many VMs you are running, you could see some blocks being in cache on one host, while it is not in cache on the other. Although this is not very likely, it could happen

Now, if you have an all-flash config this is typically no concern, and it is, for most customers, even on hybrid not a huge concern.

[IRIX201110141]

I would say on a AFA setup there is no read cache at all.

Regards.
Joerg

[baber]

So . for FTT=1 when want read a data it will just use one cache tier and cannot use both of cache tier at the same time in Hybrid is that correct ?

[depping · Accepted solution]

your question is not specific enough to answer, to be honest. it will depend on the amount of data being read. If you read 4k or 64k or basically anything less than 1mb it will most likely come from the same caching device in hybrid. 

[baber]

So If the size of data that we want read is more than 1 MB it will be use both cache tier in Hybrid vSAN

Is that correct ?

[depping · Accepted solution]

Yes