Dell PowerVault 114x - Manual (Page 5)

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each drag- and- d rop operation. The resulting file structure on the tape is shown in
Figure 4 above.
It is recommended that multi-
threaded writes be avoided as this can impact read
performance in certain circumstances as outlined in the read performance section
below.
File Read Performance
Read operations are performed at the highest negotiated transfer rate
, for LTO6 this is
up to a rate of 160 MB/s for non- compressed data. In the most optimal environments
with contiguous files the transfer time of files from LTFS media will be near the
negotiated data rate of the system with minimal read back impact for locating when
copying back multiple files. Small transfers and the beginning of large file transfers will
be slower due to the time it takes for the drive to spin up.
In the case of i
nterlaced files, the impa ct to read can be greatly affected. The impact
depends on the number of threads used to copy the data and the size of the files copied.
Generally the larger the files the worse the interlacing and the worse the read back
performance. A further explanat ion of the impact of interlacing is that for every file in a
multithread write the file is broken into smaller and smaller pieces, with the number of
threads dictating how many times the data is divided and by how much of a divide there
is between each blo ck of file data. In effect, if 10 movies were to be copied to a LTFS
directory using individual drag - and- drop threads, each movie may end up being spread
across the complete length of tape. Read of a single file will require hundreds of read - >
locate - > pause sequences to retrieve the entire file.
File Access times from Mounted and Active State
File access times are not affected by the manner in which the files have been saved to
tape (contiguous or interlaced) . LTFS uses the location on tape indicated in the
metadata, as a way to accelerate the positioning of the tape for read. LTFS positions the
head in the required region of tape and issues a SCSI locate command to find the
required file.
GUI File System tips
The graphical interfaces of most operating systems allow for display of the metadata
related to the files in the file system. The degree at which the data is displayed is dictated
by the user settings in the GUI. Certain settings can cause a slower response in the LTFS
implementation and it is recommended that they not be used.
In all GUI displays it is recommended that the settings be set to display the filename only.
It is highly recommended that the GUI specifically be set to not display icons as this will
slow the response to a directory open in LTFS
because LTFS must retrieve the icon being
used for each file.