From 452517900b740c1fd397a45dd60e21139e4ff858 Mon Sep 17 00:00:00 2001 From: cracauer Date: Thu, 13 Apr 2006 20:35:31 +0000 Subject: Make CCD be able to read and write Linux software raids. Supported for raid-0 with disks, raid-1 with 2 disks. Manpages have examples, warnings etc. Test scripts on http://www.cons.org/cracauer/ccdconfig-linux/ Reviewed by: alfred --- share/man/man4/ccd.4 | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) (limited to 'share') diff --git a/share/man/man4/ccd.4 b/share/man/man4/ccd.4 index 4ff4002..d49a82d 100644 --- a/share/man/man4/ccd.4 +++ b/share/man/man4/ccd.4 @@ -173,6 +173,34 @@ You cannot replace a disk in a mirrored .Nm partition without first backing up the partition, then replacing the disk, then restoring the partition. +.Ss Linux compatibility +The Linux compatibility mode does not try to read the label that Linux' +md(4) driver leaves on the raw devices. You will have to give the order +of devices and the interleave factor on your own. When in Linux +compatibility mode, ccd will convert the interleave factor from Linux +terminology. That means you give the same interleave factor that you +gave as chunk size in Linux. +.Pp +If you have a Linux md(4) device in "legacy" mode, do not use the +CCD_LINUX flag in +.Xr ccdconfig 8 . +Use the CCD_NO_OFFSET flag instead. In that case you have to convert +the interleave factor on your own, usually it is Linux' chunk size +multiplied by two. +.Pp +Using a Linux raid this way is potentially dangerous and can destroy +the data in there. Since FreeBSD does not read the label used by +Linux, changes in Linux might invalidate the compatibility layer. +.Pp +However, using this is reasonably safe if you test the compatibility +before mounting a raid read-write for the first time. Just using +ccdconfig without mounting does not write anything to the Linux raid. +Then you do a fsck.ex2fs on the ccd device using the -n flag. You can +mount the filesystem readonly to check files in there. If all this +works, it is unlikely that there is a problem with ccd. Keep in mind +that even when the Linux compatibility mode in ccd is working +correctly, bugs in FreeBSD's ex2fs implementation would still destroy +your data. .Sh WARNINGS If just one (or more) of the disks in a .Nm -- cgit v1.1