Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
cancel

Context-aware DRE caching and Uni-directional DRE

Hi,

Uni-directional DRE impacts the way that signatures and and Chunks are stored :

  • On the Datacenter WAAS only the signatures are stored (in memory)
  • On the Branch WAAS both signatures (in memory) and chunks (on disk) are stored

How can the Datacenter WAAS determine if the data has previously been seen (and generate a signature), when it does not have the original data stored ?

If data chunks aren't stored, then only the signatures can be used to determine if the data has been previously seen :

Does this mean that signatures are uniquely generated from data (i.e. two different data chunks can't generate the same signature) ?

Best Regards

Finn Poulsen

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Context-aware DRE caching and Uni-directional DRE

Hi Finn,

So, here is the answer to your questions.

1. DC-WAAS will not remove the signature unless asked to do so or eviction kicks in.

2. If peer A has no signature / chunk, it will generate NACK to DC WAAS for the signature packet and then DC-WAAS will send out data to peer A if it has signature.

Hope thsi answers your questions.

PS: Please mark this as Answered, if this answers your question.

5 REPLIES
Cisco Employee

Context-aware DRE caching and Uni-directional DRE

Hi Finn,

Answers for you:

How can the Datacenter WAAS determine if the data has previously been seen (and generate a signature), when it does not have the original data stored ?

Ans: This is uni-Directional so DC WAAS is not going to store it on disk.

If data chunks aren't stored, then only the signatures can be used to determine if the data has been previously seen. Does this mean that signatures are uniquely generated from data (i.e. two different data chunks can't generate the same signature) ?

Ans: Yes, signatures are unique but will be same from same chunk of data.

Hope this helps.

Regards.

PS: Please mark this as Answered, if this answers your question.

Context-aware DRE caching and Uni-directional DRE

Hi Bhavin,

Thanks - just to fully understand the uni-directional behaviour (internally in the Datacenter WAAS) :

A) TCP Session 1 to peer A flows through DC-WAAS, which (consider an empty DRE cache) :

  1. Generates a signature on a chunk
  2. stores the signature for peer A
  3. sends the signature and chunk to peer A
  4. "deletes" the chunk internally

B) TCP session 2 to same peer flows through DC-WAAS

  1. Generates a signature on a chunk
  2. compares the new generated signature with all Peer A's signatures and finds a match (since exactly this chunk is the same as previouly sent in A3 above)
  3. sends only the signature to peer A

....

C) Some time later WAAS Peer A evicts the chunk due to DRE aging :

  1. Peer A signals to DC-WAAS that this signature is no longer valid for this peer (itself)
  2. DC-WAAS removes this signature from the signature table related to peer A only

Questions :

1) Is above described behaviour basically correct (don't need entire mechanism :-) ?

2) How is this signalling, described in C) above, done - if my description is correct ?

Best regards and thanks

Finn Poulsen

Cisco Employee

Context-aware DRE caching and Uni-directional DRE

Hi Finn,

I need to work on this with internal resources here to answer your questions. I will post the update for you soon.

Thanks,

Bhavin.

Cisco Employee

Context-aware DRE caching and Uni-directional DRE

Hi Finn,

So, here is the answer to your questions.

1. DC-WAAS will not remove the signature unless asked to do so or eviction kicks in.

2. If peer A has no signature / chunk, it will generate NACK to DC WAAS for the signature packet and then DC-WAAS will send out data to peer A if it has signature.

Hope thsi answers your questions.

PS: Please mark this as Answered, if this answers your question.

Context-aware DRE caching and Uni-directional DRE

Thanks a lot

Finn

912
Views
0
Helpful
5
Replies
CreatePlease to create content