SFA Appliance Structure.¶
Structure.¶SFA appliance is the server, which integrates reliable data storage with SFA services.
It provides the following services:
- Cache written files.
- Pack written files and write packages to tapes.
- Stage packaged files from tape into read cache for the consequent delivery to clients.
Cache data storage is provided by ZFS on Linux service.Enstore SFA components running on SFA appliance are.
- Disk Movers providing delivery and caching of client files in local ZFS storage (write cache).
- Migrators providing packaging of written to cache files and writing them to tapes and staging files from tapes into local ZFS storage (read cache).
Cache usage considerations.¶
SFA is implemented so that it can use separate write and read cache or combined.
If write and read caches are separate the written files get purged as soon as they are packaged written to tape.
If enstore is used with dcache packaged files get read into dcache pools and treated there. So there is a little use of read cache.
So, in average, the read and write SFA cache sizes are 0.
For effective use of storage it is better to have a common cache for writes and reads. In this case cache will not be cleaned until it reaches
watermark. The watermark can be set pretty low to accommodate with spikes in data write requests. It could be set to 70 or 60%.