SYSTEMD-READAHEAD-(8)

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)