On Jan 11, 2010, at 8:05 AM, bank kus wrote: > As of 2009.06 what is the policy with reordering ZFS file reads i.e., > consider the following timeline: > T0: Process A issues read of size 20K and gets its thread switched out > > T1: Process B issues reads of size 8 bytes and gets its thread switched out > > Are the 8 byte reads from B going to fall in queue _behind_ A if:
Order is not preserved in either the OS or the device. The data will be cached in the device, ZFS vdev cache, ARC, and L2ARC. At some point in time, the data will be evicted, depending on the cache demand and policies. It is unlikely that the media will be read twice if both reads are issued at near the same time. > --> if A and B are from separate users? > --> If B is from the system process? Doesn't matter. None of those caches are tagged by pid. -- richard
