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Alexander Moibenko, 01/14/2016 05:01 PM

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h1. SFA Appliance Structure.
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h2. Structure.
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SFA appliance is the server, which integrates reliable data storage with SFA services.
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It provides the following services:
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# Cache written files.
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# Pack written files and write packages to tapes.
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# Stage packaged files from tape into read cache for the consequent delivery to clients.
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Cache data storage is provided by ZFS on Linux service.
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Enstore SFA components running on SFA appliance are.
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# Disk Movers providing delivery and caching of client files in local ZFS storage (write cache).
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# Migrators providing packaging of written to cache files and writing them to tapes and staging files from tapes into local ZFS storage (read cache).
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h2. Cache usage considerations.
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SFA is implemented so that it can use separate write and read cache or combined.
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If write and read caches are separate the written files get purged as soon as they are packaged written to tape.
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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.
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So, in average, the read and write SFA cache sizes are 0.
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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
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watermark. The watermark can be set pretty low to accommodate with spikes in data write requests. It could be set to 70 or 60%.
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h2. Hardware considerations.