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SYSTEMD−READAHEAD−

NAME

systemd-readahead-replay.service, systemd-readahead-collect.service, systemd-readahead-done.service, systemd-readahead-done.timer, systemd-readahead − Disk read ahead logic

SYNOPSIS

systemd−readahead−replay.service

systemd−readahead−collect.service

systemd−readahead−done.service

systemd−readahead−done.timer

/usr/lib/systemd/systemd−readahead

DESCRIPTION

systemd−readahead−collect.service is a service that collects disk usage patterns at boot time. systemd−readahead−replay.service is a service that replays this access data collected at the subsequent boot. Since disks tend to be magnitudes slower than RAM this is intended to improve boot speeds by pre−loading early at boot all data on disk that is known to be read for the complete boot process.

systemd−readahead−done.service is executed a short while after boot completed and signals systemd−readahead−collect.service to end data collection. On this signal this service will then sort the collected disk accesses and store information about them disk in /.readahead.

Normally, both systemd−readahead−collect.service and systemd−readahead−replay.service are activated at boot so that access patterns from the preceding boot are replayed and new data collected for the subsequent boot. However, on read−only media where the collected data cannot be stored it might be a good idea to disable systemd−readahead−collect.service.

On rotating media, when replaying disk accesses at early boot systemd−readahead−replay.service will order read requests by their location on disk. On non−rotating media, they will be ordered by their original access timestamp. If the file system supports it systemd−readahead−collect.service will also defragment and rearrange files on disk to optimize subsequent boot times.

SEE ALSO

systemd(1)

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