Toby Thain wrote: > On 30-Sep-08, at 6:58 AM, Ahmed Kamal wrote: > > >> Thanks for all the answers .. Please find more questions below :) >> >> - Good to know EMC filers do not have end2end checksums! What about >> netapp ? >> > > Blunty - no remote storage can have it by definition. The checksum > needs to be computed as close as possible to the application. What's > why ZFS can do this and hardware solutions can't (being several > unreliable subsystems away from the data). > > --Toby > >
Well.... That's not _strictly_ true. ZFS can still munge things up as a result of faulty memory. And, it's entirely possible to build a hardware end2end system which is at least as reliable as ZFS (e.g. is only faultable due to host memory failures). It's just neither easy, nor currently available from anyone I know. Doing such checking is far easier at the filesystem level than any other place, which is a big strength of ZFS over other hardware solutions. Several of the storage vendors (EMC and NetApp included) I do believe support hardware checksumming over on the SAN/NAS device, but that still leaves them vulnerable to HBA and transport medium (e.g. FibreChannel/SCSI/Ethernet) errors, which they don't currently have a solution for. I'd be interested in seeing if anyone has statistics about where errors occur in the data stream. My gut tells me that (from most common to least): (1) hard drives (2) transport medium (particularly if it's Ethernet) (3) SAN/NAS controller cache (4) Host HBA (5) SAN/NAS controller (6) Host RAM (7) Host bus issues -- Erik Trimble Java System Support Mailstop: usca22-123 Phone: x17195 Santa Clara, CA Timezone: US/Pacific (GMT-0800) _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
