Date: Tue, 07 Dec 2010 22:24:25 -0500 From: Boris Kochergin <spawk@acm.poly.edu> To: Charles Sprickman <spork@bway.net> Cc: freebsd-fs@freebsd.org Subject: Re: "sharing" hot spares? Message-ID: <4CFEFA69.8020904@acm.poly.edu> In-Reply-To: <alpine.OSX.2.00.1012072110160.43483@hotlap.local> References: <alpine.OSX.2.00.1012072110160.43483@hotlap.local>
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On 12/07/10 21:24, Charles Sprickman wrote: > All, > > This is probably an odd question... We're extensively using ZFS on a > bunch of 1U boxes and packing all the drive bays full. This is all > SATA, so I would like to have hot spares available, but without > migrating everything to new enclosures, I'm not seeing an easy way to > deal with this. > > Is there anything out there that would allow me to export a few drives > from another box as block devices that the other boxes could > *temporarily* use as hot spares until someone onsite could physically > do a drive swap? > > I would also really like to share one drive amongst multiple hosts - I > am making the likely over-optimistic assumption that I'll be dealing > with no more than one drive failure per say, 3 hosts at a time. > > -hast doesn't seem quite right, as it's more about clustering than > just exporting a device. > > -geom-gate looks like it might fill the bill, but I'm unsure as to > whether it would allow an export of one drive to more than one box, > and if it did, if it would have any way of letting a second host know > the drive is busy. > > -iscsi seems like it might work as well, but I'm leery of anything not > deemed stable/supported enough to be in the base system. > > Anything else? > > I'm also totally clueless as to how zfs would deal with having one > drive coming over the network while the others are local. I assume it > should work. > > Also if there was a reboot while it was running with a disk from this > network spare "pool", could zfs then find the network drive it was > using since it will be available later than the local drives? > > This whole scheme is just something that came to me a few minutes ago, > my apologies if it sounds a bit nuts. Just trying to solve an > interesting problem. > > Thanks, > > Charles > _______________________________________________ > freebsd-fs@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-fs > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org" Ahoy. a geom_gate device can indeed be exported to multiple hosts, and ZFS over geom_gate works fine. As for synchronization, you don't get any with geom_gate itself--you can attach a device for writing from multiple hosts. However, I also believe ZFS will not use a disk (unless maybe you force it) if it currently has ZFS metadata on it. If this is the case, you could leave it to ZFS not to use a spare that's already in use by another host. In this scenario, I suppose there might exist a race condition where two machines' disks fail at the same time, and they attempt to use the geom_gate spare at the same time. I'll leave it to you to decide whether to worry about this. -Boris
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