On Wed, 16 Jun 2010, Arne Jansen wrote:
Please keep in mind I'm talking about a usage as ZIL, not as L2ARC or main pool. Because ZIL issues nearly sequential writes, due to the NVRAM-protection of the RAID-controller the disk can leave the write cache enabled. This means the disk can write essentially with full speed, meaning 150MB/s for a 15k drive. 114000 4k writes/s are 456MB/s, so 3 spindles should do.
Huh? What does the battery backed memory of a RAID-controller have to do with the unprotected memory of a hard drive? This does not compute. The flushes that the RAID-controller acks need to be ultimately delivered to the disk or else there WILL be data loss. The RAID controller should not purge its own record until the disk reports that it has flushed its cache. Once the RAID controller's cache is full, then it should start stalling writes.
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
