>>> Can AFS cache be placed on any local filesystem like ZFS, VxFS or >>> UFS+logging? >>> >> >> ZFS and UFS have been used (with and without logging). I'm not sure if >> anyone has tried to use VxFS, but in theory I think it should work as >> our cache I/O mechanisms are supposed to be FS-agnostic. >> >> Note that there is a known (unfixable) issue with ZFS caches that can >> cause them to take up far more disk space than you have configured. >> >> <http://www.openafs.org/pipermail/openafs-devel/2009-September/017033.html> >> has some information. Decreasing the ZFS recordsize makes it not as bad, >> though the issue is still always there. >> >> > > This should't be a big issue. You can always set recordsize to something > smaller. > Well, one could even enable compression on zfs (depending on what data is > being cached). > From the afs point of view as someone else suggested instead of truncating a > file we would create a new one and unlink the old one. > > Actually I believe there is another way which is less expensive. The > underlying problem is that once zfs sets a recordsize for a given file it > will stick to it forever. So if you create a new file and initially write > more than 128KB of data with a default recordsize of 128KB zfs will use a fs > blocksize of 128KB, even if file is truncated later on. However if you would > create a file and initially write only lets say 1KB it will choose a 1KB > recordsize and then stick to it regardless of how much data is being > written. But then it is easier for a sysadmin to just limit the recordsize > to 8kb (or 1kb, or whatever) I guess. Afsd could check recordsize during > startup and issue a warning with recommendation to lower it to a smaller > value.
No, that is not how it works. A file will stick to the recordsize that was set for the filesystem when the file was created, regardless of the size of inital writes. A file smaller than recordsize will have a smaller record but that will grow to recordsize when you write more data. _______________________________________________ OpenAFS-devel mailing list [email protected] https://lists.openafs.org/mailman/listinfo/openafs-devel
