On Sat, 29 Aug 2009, David Bond wrote:
Ok, so when the chache fills and needs to be flushed, when the flush occurs it locks access to it, so no read? or writes can occur from cache, and as everything will go through the arc, nothing can happen until the arc has finished its flush.
It has not been proven that reads from the ARC stop. It is clear that reads from physical disk temporarily stop. It is not clear (to me) if reads from physical disk stop because of the huge number of TXG sync write operations (up to 5 seconds worth) which are queued prior to the read request, or if reads are intentionally blocked due to some sort of coherency management.
And to compensate for this, I would have to either reduce the cache size to one that is small enough that the disk array can write it at such a speed that the pauses are reduced to ones that are not really noticable.
That would work. There is likely to be more total physical I/O though since delaying the writes tends to eliminate many redundant writes. For example, an application which re-writes the same file over and over again would be sending more of that data to physical disk.
Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
