Date: Sat, 2 Jul 2016 17:03:50 +0200 From: Ben RUBSON <ben.rubson@gmail.com> To: freebsd-fs@freebsd.org Subject: Re: HAST + ZFS + NFS + CARP Message-ID: <868B90CB-828F-48E8-B678-50FC1BB52FAE@gmail.com> In-Reply-To: <E9A65461-CD42-4CBD-9C22-87E1B9D5A4EA@gmail.com> References: <20160630144546.GB99997@mordor.lan> <71b8da1e-acb2-9d4e-5d11-20695aa5274a@internetx.com> <AD42D8FD-D07B-454E-B79D-028C1EC57381@gmail.com> <20160630153747.GB5695@mordor.lan> <63C07474-BDD5-42AA-BF4A-85A0E04D3CC2@gmail.com> <678321AB-A9F7-4890-A8C7-E20DFDC69137@gmail.com> <20160630185701.GD5695@mordor.lan> <FD296976-0250-4DA7-BB56-68F43B62C19B@ixsystems.com> <E9A65461-CD42-4CBD-9C22-87E1B9D5A4EA@gmail.com>
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> On 01 Jul 2016, at 20:23, Ben RUBSON <ben.rubson@gmail.com> wrote: >=20 >=20 >> On 01 Jul 2016, at 19:54, Jordan Hubbard <jkh@ixsystems.com> wrote: >> (...) >> And yes, of course one can layer additional things on top of iSCSI = LUNs, just as one can punch through LUNs from older SAN fabrics and put = ZFS pools on top of them (been there, done both of those things), though = of course the additional indirection has performance and debugging = ramifications of its own (when a pool goes sideways, you have additional = things in the failure chain to debug). ZFS really likes to =E2=80=9Cown = the disks=E2=80=9D in terms of providing block-level fault tolerance and = predictable performance characteristics given specific vdev topologies, = and once you start abstracting the disks away from it, making statements = about predicted IOPs for the pool becomes something of a =E2=80=9C???=E2=80= =9D exercise. >=20 > Would you say that giving an iSCSI disk to ZFS hides some details of = the raw disk to ZFS ? > I though that iSCSI would have been a totally "transparent" layer, = transferring all ZFS requests to the raw disk, giving back the answers, = hiding anything. =46rom #openzfs : A: typically iSCSI disks still appear as "physical" disks to the OS = connecting to them. you can even get iSCSI servers that allow things = like SMART pass-thru Q: so ZFS will be as happy with iSCSI disks as if it used local disks ? = or will it miss something ? A: no, and ZFS isn't "unhappy" per se. but there are optimizations it = applies when it knows the disks belong to ZFS only Q: and using iSCSI disks, ZFS will not apply these optimizations (even = if these iSCSI disks are only given to ZFS) ? ie, will ZFS know these = iSCSI disks belong to ZFS only ? A: if it looks like a physical disk, if it quacks like a physical = disk...=
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