Date: Tue, 26 Dec 2017 18:09:01 +0100 From: "O. Hartmann" <ohartmann@walstatt.org> To: Allan Jude <allanjude@freebsd.org> Cc: freebsd-current@freebsd.org Subject: Re: ZFS: alignment/boundary for partition type freebsd-zfs Message-ID: <20171226180928.21654d9d@thor.intern.walstatt.dynvpn.de> In-Reply-To: <bf2738b0-1774-af26-fd1e-151b6bd66c52@freebsd.org> References: <20171226172521.611a89b0@thor.intern.walstatt.dynvpn.de> <bf2738b0-1774-af26-fd1e-151b6bd66c52@freebsd.org>
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--Sig_/Cvz1M0mb_N7h_yf_B8_YDGc Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Am Tue, 26 Dec 2017 11:44:29 -0500 Allan Jude <allanjude@freebsd.org> schrieb: > On 2017-12-26 11:24, O. Hartmann wrote: > > Running recent CURRENT on most of our lab's boxes, I was in need to rep= lace and > > restore a ZFS RAIDZ pool. Doing so, I was in need to partition the disk= s I was about > > to replace. Well, the drives in question are 4k block size drives with = 512b emulation > > - as most of them today. I've created the only and sole partiton on eac= h 4 TB drive > > via the command sequence > >=20 > > gpart create -s GPT adaX > > gpart add -t freebsd-zfs -a 4k -l nameXX adaX > >=20 > > After doing this on all drives I was about to replace, something drove = me to check on > > the net and I found a lot of websites giving "advices", how to prepare = large, modern > > drives for ZFS. I think the GNOP trick is not necessary any more, but m= any blogs > > recommend to perform > >=20 > > gpart add -t freebsd-zfs -b 1m -a 4k -l nameXX adaX > >=20 > > to put the partition boundary at the 1 Megabytes boundary. I didn't do = that. My > > partitions all start now at block 40. > >=20 > > My question is: will this have severe performance consequences or is th= at negligible? > >=20 > > Since most of those websites I found via "zfs freebsd alignement" are f= rom years ago, > > I'm a bit confused now an consideration performing all this days-taking= resilvering > > process let me loose some more hair as the usual "fallout" ... > >=20 > > Thanks in advance, > >=20 > > Oliver > > =20 >=20 > The 1mb alignment is not required. It is just what I do to leave room > for the other partition types before the ZFS partition. >=20 > However, the replacement for the GNOP hack, is separate. In addition to > aligning the partitions to 4k, you have to tell ZFS that the drive is 4k: >=20 > sysctl vfs.zfs.min_auto_ashift=3D12 >=20 > (2^12 =3D 4096) >=20 > Before you create the pool, or add additional vdevs. >=20 I just checked with "zdb" what ashift is reported to my pool(s) and the res= ult claims to be "ashift: 12". --=20 O. Hartmann Ich widerspreche der Nutzung oder =C3=9Cbermittlung meiner Daten f=C3=BCr Werbezwecke oder f=C3=BCr die Markt- oder Meinungsforschung (=C2=A7 28 Abs.= 4 BDSG). --Sig_/Cvz1M0mb_N7h_yf_B8_YDGc Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- iLUEARMKAB0WIQQZVZMzAtwC2T/86TrS528fyFhYlAUCWkKCSAAKCRDS528fyFhY lF/0Af97Krwtkr9sM6lX8PzFBTBHQI+guJHkdZcViQDHRRH8nKJXf6F9MZj0lpKA FCVn1DkzpzRoIirwi/Dkwhl46Pr8AgCI7huGnhXuXOK6d8lurtr25A5nRAC6/LQJ Q/fzs/y6FGlr+2Q9gsNgMKu9C3qyxA4i+jOvbxlO3EZoBDw54CkS =5gGp -----END PGP SIGNATURE----- --Sig_/Cvz1M0mb_N7h_yf_B8_YDGc--
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