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darminm

82 Posts

680

October 13th, 2008 04:00

CPM - How many files in the cluster?

After an app writes a file to a virtual pool...how many copies will there actually exist? 2 or 4?

This would be on a cluster that has 4 nodes...2 access & 2 storage nodes.

giadarola

60 Posts

October 13th, 2008 06:00

For data that is written in CPM (Mirrored) there will be a total of 4 files: The actual data file (called a BLOB) which will be mirrored (origianl + copy = 2) + the CDF (also called the C-Clip) which also is mirrored = 4 files for every write.

For Clusters that are storing data in CPP (Parity) format there will be the original file (BLOB) chunked out to 6+ 1 = 7 + the C-Clip in mirrored format for a total of 9 files for ever write.

darminm

82 Posts

October 14th, 2008 03:00

Thank you both. Very helpful!

mikehorgan

47 Posts

October 14th, 2008 03:00

Just for completeness' sake, it should be pointed out that Centera applications can choose to 'embed' small blobs (up to 100KB) directly into the C-Clip file (CDF) which eliminates the object count associated with storing the blob (and also provides a performance increase). If this is the case, only 2 objects (mirrored copies of the CDF) are generated for a 'file' regardless of protection strategy (CPM or CPP).

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