15 February 2011

ATLAS Tape Store file sizes

Here is the profile of the files that are stored by ATLAS at RAL.

Minimum file size stored for both DATA and MC is 20 bytes

Maximum file size stored is:[12963033040,11943444017] or [13GB,11.9GB]

Average file size is: [1791770811,637492224] or [1.79GB,637MB]
The median filesize for [DATA,MC] are [2141069172,602938704] ([2.1GB,602MB] ) .

Number of files stored is: [282929,672707] of [DATA,MC] files for a total size of [506943923754228,428845482035182] or [507TB,428TB] in total.

[37,5687] files in [DATA,MC] are zero sized ( but we don't have to worry about them as the tape system does not copy 0 size files to tape.

However these are better than the [538,537] 20 byte files which have been migrated to tape (these are 0B sized log files which have then been "tar" and "gzip"ed before being written into Castor.)

The modal average filesizes are [26860316,0]Bytes with [286,5687] files of this size.
These are most likely failed transfers, next modal filesize with 537 entries are files with a size of 20bytes, but theses are just test files. The first genuine modal filesize jointly have 13 files and have size 19492 an 19532 Bytes.

Whereas [254040,626556] have a unique filesize (this equates to only [89.8,93.1] percent of files having a unique file size so checksum is important!!)

Could be worse though , one VO successfully stored a file that is one byte in size (the fact the header and footer on tape file and compressing the file actually increased the size of file actually stored on tape......)

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