User`s guide

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5: Adding and Removing Clips
Clip Alignment
Certain clips might need to be aligned in the filesystem for enhanced performance. In
single-disk systems, media files are aligned only with the filesystem’s block size so that
only one I/O operation is needed to access the data.
In multidisk, RAID striped systems, the media files must also be aligned with the stripes.
When the SGI Media Server is used to record media, it automatically places the media
data in the correct, aligned locations on the disk.
Degree of Alignment
Frame-oriented media data in an intraframe clip is aligned along the following two
boundaries:
• Minor alignment boundary
• Major alignment boundary
A single element of a frame (a video field or audio chunk) never crosses a minor or major
alignment boundary. The SGI Media Server will not do a read or write operation to the
clip media file that crosses a major alignment boundary.
Minor Alignment
The minor alignment matches the greater of the filesystem block size or the system
memory page size. On the SGI Media Server, the minor alignment is usually 16 KB,
unless a larger filesystem block size was used.
Major Alignment
The major alignment matches the stripe size of the disk volume that holds the clip cache
filesystem.
If the clip cache resides on a single disk, no major alignment is required.
If the clip cache resides on a single RAID subsystem, major alignment is required for
efficient I/O access to the media data. Create a real-time filesystem on the RAID LUN
and set the real-time extent size of the XFS filesystem to the desired I/O operation size.