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Re: zfs: 9 vs current, and ZIL/L2ARC on ssd?

	hello Greg.  Zfs seems to be much more stable in -current than 9.x.  In particular, if
you're using xen, then you definitely want -current because ZFS and xen under 9.x use different
maxphys values for data transfers, which leads to a lot of corruption and crashes when using
zfs as backingstore for xen domains.  Also, under -current, dom0 can be a multi-vcpu system,
which should help performance significantly when it comes to i/o on the domu's, especially if
running any kind of hvm or pvh domain.

Hope that helps.


On Feb 11,  1:17pm, Greg Troxel wrote:
} Subject: zfs: 9 vs current, and ZIL/L2ARC on ssd?
} --=-=-=
} Content-Type: text/plain
} I am about to try to use zfs for the first time and have a few
} questions.
} I have a machine that is running NetBSD-9/amd64 with 2 cores, 8G of RAM,
} a single 1T SSD, with a smallish root/swap/usr, and about 870 GiB free
} intended for zfs.  I am heading for one po0l that is not raid at all.
} I'm not all that worried about transitions or stability; this is a build
} machine for packages, not particularly precious, and it being down for a
} week while I fix it is no big deal.
} I will likely pivot the machine to be xen dom0; I hope that doesn't
} matter much (other than 1 core only in the dom0).  Or I might use nvmm,
} or both.
} I might add a spinning disk later, either internal or USB.  (I realize
} that there, I probably want both ZIL and L2ARC on SSD.  I would rather
} move bits later than do things now to ease that, since I do not have an
} actual plan.)
} My questions are:
}   Is 9/current close enough to the same zfs code that it doesn't matter
}   which I run?  If I'm inclined to run current for other reasons, is
}   that a bad idea zfs-wise?
}   I understand that zfs has an intent log always, and that can be within
}   the pool, or one can add a ZIL device.  With the pool having one
}   device which is an SSD, I see no point in partitioning off part of
}   that SSD to be the ZIL.
}   I understand that zfs has ARC in RAM, and can have L2ARC on disk.
}   Given that the pool is on SSD, it seems pointless to split off some
}   for L2ARC.
} My expected answers are:
}   The code is basically the same and it doesn't really matter but
}   probably current has some bugfixes 9 doesn't.  There's no reason
}   current is scary becuase of zfs.
}   There is no point in a ZIL on the same SSD as the pool.
}   There is really no point in L2ARC on the same SSD as the pool.
} Corrections/clues appreciated.

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