If MAGICK_IO_FSYNC is set to TRUE, then GraphicsMagick will request that the output file is fully flushed and synchronized to disk when it is closed. This incurs a performance penalty, but has the benefit that if the power fails or the system crashes, the file should be valid on disk. If image files are referenced from a database, then this option helps assure that the files referenced by the database are valid.

MAGICK_IOBUF_SIZE

The amount of I/O buffering (in bytes) to use when reading and writing encoded files. The default is 16384, which is observed to work well for many cases. The best value for a local filesystem is usually the the native filesystem block size (e.g. 4096, 8192, or even 131,072 for ZFS) in order to minimize the number of physical disk I/O operations. I/O performance to files accessed over a network may benefit significantly by tuning this option. Larger values are not necessarily better (they may be slower!), and there is rarely any benefit from using values larger than 32768. Use convert's -verbose option in order to evaluate read and write rates in pixels per second while keeping in mind that the operating system will try to cache files in RAM.

MAGICK_LIMIT_DISK

Maximum amount of disk space allowed for use by the pixel cache.