From owner-freebsd-questions@freebsd.org Sat Oct 3 03:20:48 2015 Return-Path: Delivered-To: freebsd-questions@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id F07D0A0D120 for ; Sat, 3 Oct 2015 03:20:47 +0000 (UTC) (envelope-from wam@hiwaay.net) Received: from fly.hiwaay.net (fly.hiwaay.net [216.180.54.1]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id BEBFA1D00 for ; Sat, 3 Oct 2015 03:20:47 +0000 (UTC) (envelope-from wam@hiwaay.net) Received: from kabini1.local (dynamic-216-186-213-32.knology.net [216.186.213.32] (may be forged)) (authenticated bits=0) by fly.hiwaay.net (8.13.8/8.13.8/fly) with ESMTP id t933Kin6027124 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES128-SHA bits=128 verify=NO) for ; Fri, 2 Oct 2015 22:20:45 -0500 Subject: Re: Geom question References: <560EDE45.3040605@hiwaay.net> <3D81C7BC-1A31-4046-88B7-50F25EA3B952@ccsys.com> <560EEE5F.3080904@hiwaay.net> <560F04A5.1060102@ccsys.com> Cc: FreeBSD Questions !!!! From: "William A. Mahaffey III" Message-ID: <560F498C.7090707@hiwaay.net> Date: Fri, 2 Oct 2015 22:26:14 -0453.75 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <560F04A5.1060102@ccsys.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 03 Oct 2015 03:20:48 -0000 On 10/02/15 17:33, Chad J. Milios wrote: > On 10/2/2015 5:25 PM, Warren Block wrote: >> On Fri, 2 Oct 2015, William A. Mahaffey III wrote: >> >>> On 10/02/15 15:31, Chad J. Milios wrote: >>>>> On Oct 2, 2015, at 3:41 PM, William A. Mahaffey III >>>>> wrote: >>>>> >>>>> I am prepping to provision 2 boxen w/ FreeBSD 9.3R, preferably >>>>> from a thumb drive. I would like to add a 'utils' directory w/ >>>>> some scripts I wrote to automate the partitioning/slicing of the >>>>> HDD's (2X on 1 box, 8X on the other), & also accumulate output >>>>> from the install process in case questions arise. To that end, I >>>>> am planning on partitioning/slicing a thumb drive, prepping it to >>>>> be bootable following examples on the gpart man page, & copying >>>>> verbatim stuff from the memstick.img for 9.3R that I downloaded a >>>>> while back, as well as adding my utils directory. Reading up on >>>>> gpart & geom raises 1 question: can I do all these preps on a disk >>>>> image file I create w/ dd, or do i do them in place on the target >>>>> memstick, then dd the results onto an on-disk image for >>>>> safekeeping ? Put another way, can a disk image created by dd be a >>>>> 'geom' for gpart ? TIA & have a good one. >>>>> >>>>> -- >>>>> >>>>> William A. Mahaffey III >>>> In a way, yes. `mdconfig -f filename` will make your file >>>> accessible as a virtual device. >>>> >>> >>> Then to be accessed as /dev/md0 ? Any other clues/gotchas :-) ? >>> Thanks & TIA & have a good one. >> >> GPT does not work well with that. If the target device is larger, >> the backup GPT that is supposed to go at the very end of the disk >> ends up someplace before that. If the target device is smaller, >> well, it won't work at all. > > he's right. unless your md is exactly the correct total size, to the > byte, the backup GPT header will be lost after copying to a different > device. alas, it is a backup after all, unless/until the primary > header suffers calamity, it'll cause you no grief. for the > thorough/cautious `gpart recover da0` will fix it afterward, (assuming > your data fits on the target and da0 is your usb stick). More > problematic is that block sizes might mismatch. use `diskinfo -v > $GEOM` to investigate, for each of your various top-level values for > $GEOM. the "sectorsize" is the logical block size, which if mismatched > can cause you overall configuration problems / total non-function. the > "stripesize" is [if it can be detectected] your physical hardware > blocksize which if mismatched will work but with abysmal performance. > if stripesize is zero then nine times out of ten you can assume its > the same as sectorsize. Then `gnop` is a geom layer utility for you > that can fake different block sizes, so if you gnop your md0 to match > your da0 you'll be able to make a proper image on md0 to transfer > later to da0 I think I am good here, although I took no explicit steps to set sector sizes (although I did carefully size md0 to (as exactly as possible) da0): [root@kabini1, /etc, 5:42:20pm] 779 % diskinfo -v /dev/md0 /dev/md0 512 # sectorsize 3878682624 # mediasize in bytes (3.6G) 7575552 # mediasize in sectors 0 # stripesize 0 # stripeoffset [root@kabini1, /etc, 10:21:06pm] 780 % diskinfo -v /dev/md1 /dev/md1 512 # sectorsize 717373440 # mediasize in bytes (684M) 1401120 # mediasize in sectors 0 # stripesize 0 # stripeoffset [root@kabini1, /etc, 10:21:18pm] 781 % diskinfo -v /dev/da0 /dev/da0 512 # sectorsize 3878682624 # mediasize in bytes (3.6G) 7575552 # mediasize in sectors 0 # stripesize 0 # stripeoffset 471 # Cylinders according to firmware. 255 # Heads according to firmware. 63 # Sectors according to firmware. C1005473D05C9225 # Disk ident. [root@kabini1, /etc, 10:21:48pm] 782 % da0 is the memstick, md0 is the stuff I am prepping, md1 is the image I downloaded & will transfer to md0, along w/ some other stuff, to eventually write to da0. > >> Also, avoid using dd on SSDs. Not using a SSD here, but the warning is noted. > > dd's "conv=sparse,notrunc" mode of operation will alleviate this > problem (the problem of beating it up with writes), though it'll leave > sectors which are all zero on the source untouched on the target, > which could be undesired. on an ssd you can TRIM the whole device > first (logically zero it out without actually writing zeros) by using > `camcontrol security $DEV -U user -s foo; camcontrol security $DEV -U > user -e foo` replacing $DEV with ada0 (or your real target) to > logically erase it. It should take no more than 5 minutes. (Despite > the word "security", do not be fooled, this is a quick logical wipe > and the old data can be recovered. It can do more with other options.) > > NOTE: while you research `man camcontrol` note theres a -u in the > examples which should be -U, as I've just illustrated. This typo was > fixed in HEAD and STABLE but may be in the RELEASE you're on. > > NOTE: cheapo usb sticks probably do not support TRIM. in general > though, it's doubtful you have any real data blocks that are all zero > and the un-zero'd blocks left on the target will likely all be ignored > by virtue of the fact that the filesystem considers them free space. > >> In general, it's better to use higher-level things that understand >> the metadata, like 'gpart backup'/'gpart restore' for the >> partitioning information and dump/restore or 'zfs send' for the >> filesystems. >> 'gpart restore' can correctly restore the partitioning scheme onto a >> larger device because it understands what that data means. > > generally very good advice to follow. still, low-level hackery can be > fun and educational :) > > Cheers. > -- William A. Mahaffey III ---------------------------------------------------------------------- "The M1 Garand is without doubt the finest implement of war ever devised by man." -- Gen. George S. Patton Jr.