I have always thought that the very name "sync" is completely
misleading. The option really has nothing at all to do with IO being
synchronous or asynchronous, you can still perform IO either way ( think
non blocking and linux async IO ). What this option really does is
simply cause the cache to switch to write-through mode instead of
write-back mode.
I would have it say:
"All I/O to the file system should be synced to the disk immediately.
This effectively changes kernel disk caching for the device from
write-back to write-through mode, causing more writes to occur. Media
with limited write cycles, flash for example, will age prematurely.
Many operations may be slowed down significantly by use of this option,
but the filesystem will be more up to date in the event of a system crash."
Jonathan Andrews wrote:
The "sync" and "async" options have an impact on disk caching, yet the
manual pages avoid the term "cache" - I assume being careful to be
general about capabilities of the underlying kernel.
This does make it difficult for people trying to find options relating
to disk cache behaviour, could the "sync" and "async" options be changed
to refer to disk caches explicitly.
For example, sync currently reads.
All I/O to the file system should be done synchronously. In case of
media with limited number of write cycles (e.g. some flash drives)
"sync" may cause life-cycle shortening.
Something like this may be more meaningful to a lot of users, it may
oversimplify things with the use of the term "cache", but in most cases
its the reference users are looking (searching) for.
"All I/O to the file system should be done synchronously. This
effectively removes kernel disk caching for the device causing more
writes to occur. Media with limited write cycles, flash for example,
will age prematurely.
Thanks,
Jon
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