Xcache Possibilities and Effective Use in HPC Environments

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Xcache Possibilities
 
4th US ATLAS HPC Meeting
LBNL 
Berkeley CA
September 26, 2019
 
Andrew Hanushevsky, SLAC
 
http://xrootd.org
 
Xcache 
Xcache 
and File Transfer
 
Writable 
Xcache
Xcache
 
 
caches not supported
This is a strictly pull model
We do support FRM caching for full files
Push or pull mode possible
Not clear we need this at all
Well, beyond what we have, unless
We want a mix of Rucio and on-demand styles
Possible to do but would require FTE’s
 
September 26, 2019
 
2
 
Xcache 
Xcache 
and Remote Access
 
Perhaps the most used model
Essentially provides a CDN for remote data
Definitely, the most successful application
However
Maintaining data integrity expectations is difficult
Bad data is sticky in a cache and hard to find
Work on the way to improve this situation
Use TLS to weed out transmission errors
Overkill but the fastest solution for now
Enhance file system integrity for data at rest
 
September 26, 2019
 
3
 
Xcache 
Xcache 
and Data Streaming
 
Block caching simulates true streaming
Prefetching practically eliminates data jitter
Anything missing?
Perhaps deletion upon close
Technically, single use streams so data not needed
However, purge takes care of this eventually
Anything else to consider
Server-less Xcache may be very relevant
Certainly applicable for single use streams
 
September 26, 2019
 
4
 
Xcache 
Xcache 
and HPC
 
Optimum access uses HPC FS as cache
Xcache
Xcache
 
 
runs on DTN’s
Except for random outages best location
Allows RDMA access to fully cached files
E.g. Lustre 
Xcache
Xcache
 
 
+ direct cache access @ NERSC
Workable but not the best solution
Requires file to be fully cached 
(low probability)
Has security implications in terms of access
Best to add RDMA support to 
Xcache
Xcache
Requires additional FTE effort
 
September 26, 2019
 
5
 
Xcache 
Xcache 
Effective Use
 
The following is true of any cache
Effective use is proportional to data reuse
Only two known proposals on this
Virtual Placement from Ilija
This is simply a Rucio placement optimization
Non-simulated (i.e. real) effectiveness unknown
Cache affinity scheduling from Andy
Requires Panda to add cache as a scheduling resource
Concept is effective for LSST query scheduling
Will it work with Panda?
 
September 26, 2019
 
6
 
Xcache 
Xcache 
Optimum Workflow
 
Since we need high reuse
.
Caches most suitable to analysis
Will not help production, unless
Used as a streaming appliance for event delivery
To reduce disk usage and steady the stream
Refer to the previous slide on streaming
 
September 26, 2019
 
7
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Xcache, a versatile caching system, offers various possibilities for data transfer, remote access, data streaming, and HPC optimization. The system enables efficient data reuse and provides enhanced data integrity and accessibility features. Explore the potential applications and considerations for integrating Xcache into high-performance computing environments.

  • Caching System
  • Data Transfer
  • Remote Access
  • HPC Optimization
  • Data Streaming

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  1. Xcache Possibilities 4th US ATLAS HPC Meeting LBNL Berkeley CA September 26, 2019 Andrew Hanushevsky, SLAC http://xrootd.org

  2. Xcache and File Transfer Writable Xcache caches not supported This is a strictly pull model We do support FRM caching for full files Push or pull mode possible Not clear we need this at all Well, beyond what we have, unless We want a mix of Rucio and on-demand styles Possible to do but would require FTE s September 26, 2019 2

  3. Xcache and Remote Access Perhaps the most used model Essentially provides a CDN for remote data Definitely, the most successful application However Maintaining data integrity expectations is difficult Bad data is sticky in a cache and hard to find Work on the way to improve this situation Use TLS to weed out transmission errors Overkill but the fastest solution for now Enhance file system integrity for data at rest September 26, 2019 3

  4. Xcache and Data Streaming Block caching simulates true streaming Prefetching practically eliminates data jitter Anything missing? Perhaps deletion upon close Technically, single use streams so data not needed However, purge takes care of this eventually Anything else to consider Server-less Xcache may be very relevant Certainly applicable for single use streams September 26, 2019 4

  5. Xcache and HPC Optimum access uses HPC FS as cache Xcacheruns on DTN s Except for random outages best location Allows RDMA access to fully cached files E.g. Lustre Xcache + direct cache access @ NERSC Workable but not the best solution Requires file to be fully cached (low probability) Has security implications in terms of access Best to add RDMA support to Xcache Requires additional FTE effort September 26, 2019 5

  6. Xcache Effective Use The following is true of any cache Effective use is proportional to data reuse Only two known proposals on this Virtual Placement from Ilija This is simply a Rucio placement optimization Non-simulated (i.e. real) effectiveness unknown Cache affinity scheduling from Andy Requires Panda to add cache as a scheduling resource Concept is effective for LSST query scheduling Will it work with Panda? September 26, 2019 6

  7. Xcache Optimum Workflow Since we need high reuse . Caches most suitable to analysis Will not help production, unless Used as a streaming appliance for event delivery To reduce disk usage and steady the stream Refer to the previous slide on streaming September 26, 2019 7

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