Date: Sat, 14 Nov 1998 23:40:53 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: mike@smith.net.au (Mike Smith) Cc: peter.jeremy@auss2.alcatel.com.au, hackers@FreeBSD.ORG Subject: Re: [Vinum] Stupid benchmark: newfsstone Message-ID: <199811142340.QAA27778@usr02.primenet.com> In-Reply-To: <199811132150.NAA00549@dingo.cdrom.com> from "Mike Smith" at Nov 13, 98 01:50:40 pm
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[ ... disk-to-disk copies over the SCSI bus not involving the host ... ] > > > And it's almost impossible to find > > >spindle synchronized disks nowadays. > > > > Seagate Barracuda's support it, I assumed that the newer Seagates did > > as well. The impression I got was that all you had to do was wire the > > `spindle sync' lines from all the disks together and then designate > > all except one as a sync'd slave. Admittedly, I've never tried > > actually using it. > > Most modern "server class" SCSI disks support it. It's not useful > unless you turn off tagged queueing, caching and most other drive > performance features. Actually, I could see it being *very* useful for copying data between plexes on different volumes for the purpose of replication. Bringing a new disk online in a RAID 5 array could also use this to advantage. I don't think either of these applications actually requires that you turn off drive performance features -- though you would have to reserve tag space to not starve the sending drive. Finally, if a disk could be made to talk to itself (unlikely, but some vendor probably neglected to prevent it by checking for the same source/target ID, I hope 8-)), it would be useful for various intra-disk transfers of data, as well. > You'd have to cons a new map and have it present the scattered target > area as a linear region. This is expensive, and the performance boost > is likely to be low to nonexistent for optimal stripe sizes. > Concatenation of multiple stripe reads is only a benefit if the stripe > is small (so that concatenation significantly lowers overhead). Compared to the normal recalculation time on a new hot-swap on a large array, I would think that even though it's expensive, it would be less expensive than the alternative of having to do the same thing anyway, *and* transfer the SCSI data in an out of host memory over, best case, a PCI bus. > > What would be useful is some help (from vinum or ccd) to ensure that > > the cylinder group blocks (superblock + inode maps etc) don't cross > > stripes. > > That's something that the user should take care of. Any power-of-2 > stripe size is likely to work out OK, as CG's are currently 32MB. Hm. Maybe the tools should limit this, or at least "bitch", in the same sense that disklabel puts up little asterisks... Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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