On Thu, 8 Apr 2010, Jason S wrote:
One thing i have noticed that seems a littler different from my previous hardware raid controller (Areca) is the data is not constantly being written to the spindles. For example i am copying some large files to the array right now (approx 4 gigs a file) and my network performance is showing a transfer rate on average of 75MB/s. When i physically watch the server i only see a 1-2 second flury of activity on the drives then about 10 seconds of no activity. Is this the nature of ZFS?
Yes, this is the nature of ZFS. ZFS batches up writes and writes them in bulk. On a large memory system and with a very high write rate, up to 5 seconds worth of low-level write may be batched up. With a slow write rate, up to 30 seconds of user-level writes may be batched up.
The reasons for doing this become obvious when you think about it a bit. Zfs writes data as large transactions (transaction groups) and uses copy on write (COW). Batching up the writes allows more full-blocks to be written, which decreases fragmentation, improves space allocation efficiency, improves write performance, and uses fewer precious IOPS. The main drawback is that reads/writes are temporarily stalled during part of the TXG write cycle.
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
