Koen Smits wrote: > Areca Support: > Dear Sir, > the only difference is > in JBOD mode, controller configure all drives as passthrough disk. > in RAID mode, you have to configure passthrough disk by yourself in RAID > mode > > in other words, you can use raid with passthrough disks at saem time in > RAID mode but JBOD mode not. > > Me: > So does that mean if I use passthrough, I am not protected by the > cache/battery backup? I ask because there is an option for cache mode > when creating a passthrough disk. i.e. Write-Back or Write-Through > > > So 'passthrough' means that the controller lets the OS see the physical > disks just as they are, but with an invisible cache in between that > buffers operations. This way there is no advantage of the onboard XOR > engine, but you do profit from the intelligent cache, which is the most > important anyway imho.
Not exactly. In JBOD mode ALL disks are passed through to the OS. You cannot have RAID. The cache is set to Write-Back. In RAID mode, you can mix raid5, raid6 and Passthrough (which are like JBOD but allow writethrough or writeback cache at your discretion). > JBOD mode is at a disadvantage because in this mode the OS sees one > large drive, and is not able to stripe the data to multiple disks, not > taking advantage of the fact that you have multple spindles available. > Makes sense to me :). No, in JBOD, the OS sees all disks individually. What you are talking about is a concatenated disk set which I don't think has a raid level. > I must admit, I do like these results. Very promising. Me too, although I am not sure if I like the idea of turning off the cache flushes in ZFS. I'd be a lot happier if the Areca card would tell me how 'full' the cache was. I'd also love to know if there was a way for the disk to tell me what the status if it's own cache is. > Further tests would be using an SSD for the ZIL, testing linux and NT, > etc. But let's not go there ;). Nope :-) -D _______________________________________________ freebsd-hardware@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hardware To unsubscribe, send any mail to "freebsd-hardware-unsubscr...@freebsd.org"