Date: Sat, 29 Nov 2014 12:31:30 +0000 From: Mykola Golub <to.my.trociny@gmail.com> To: Lorenzo Perone <lopez.on.the.lists@yellowspace.net> Cc: freebsd-fs@freebsd.org Subject: Re: Mounting a filesystem on a HAST provider without HAST (was: Re: HAST, zvols, istgt and carp working...) Message-ID: <20141129123130.GA21946@gmail.com> In-Reply-To: <54785AA1.10107@yellowspace.net> References: <AANLkTim5FRJkf_S0aSV74S=JY%2Bg1DBZLhjYW7X9C0MkP@mail.gmail.com> <5477B7AF.5020802@yellowspace.net> <54785AA1.10107@yellowspace.net>
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On Fri, Nov 28, 2014 at 12:21:05PM +0100, Lorenzo Perone wrote: > The UFS filesystem on the zvol provider begins after 135168 bytes > (132KB) of hast-header. > > So I tried to create a transparent provider with gnop: > > gnop create -o 135168 /dev/zvol/rtank/vols/jail1@hellotest > > and the mount > > mount -t ufs -o ro /dev/zvol/rtank/vols/jail1@hellotest.nop /mnt > > succeeded. > > Now my new question is: Can I "safely" assume that this header is always > 132K (I assume not - it probably contains the bitmap...)? In this case, > which formula should be applied to calculate the offset? The header contains 4096 bytes of HAST metadata (METADATA_SIZE) + map, which size depends on media size and extent size. You can obtain the offset by running `hastctl dump' command (localcnt field). If you still want to calulate it yourself, see how hastctl calculates hr_localoff in sbin/hastctl/hastctl.c:create_one() with the help of sbin/hastd/metadata.c:activemap_calc_ondisk_size(). In short, you need to calculate number of extents (mediasize / extentsize) and reserve a bit for every extent in the map, rounding up to the sector size. -- Mykola Golub
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