> -----Original Message----- > From: Phillip Susi [mailto:psusi@xxxxxxxxxx] > Sent: Monday, January 14, 2013 3:45 PM > To: Tomczak, Marcin > Cc: neilb@xxxxxxx; linux-raid@xxxxxxxxxxxxxxx; Patelczyk, Maciej; > Dorau, Lukasz > Subject: Re: [PATCH] imsm: Forbid spanning between multiple > controllers. > > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On 1/14/2013 8:02 AM, Tomczak, Marcin wrote: > > Hi. Yes, mdadm will refuse any commands, when you try to use disks > > attached to multiple controllers. Also mdadm supports IMSM metadata > > only if you have a machine with Intel OROM (and the patch "Forbid > > spanning" changes nothing about it). > > Why is this? One of the nice things about dmraid was that since it > really was just software raid, if your controller blew you could > recover your data by moving the drives to another machine and still > recognize them. Why should mdadm care about the controller? > > I suppose it is nice to warn people that they are trying to create an > array that the bios won't recognize, but mdadm should not refuse to run > an array just because some hardware that is completely unnecessary is > not found. > > Hi Phillip, Mdadm does not care about the controller unless you created IMSM based RAID. Basically you can create that type of RAID *only* on Intel based platforms with OROM enabled. It's Intel solution, we support it and we maintain it. It's very specific type of metadata. We provide this functionality in Linux, Windows and OROM/uEFI. It must be compatible between all three environments. If you have dual boot machine you can safely boot into Windows and then into Linux and your RAID Volume will be in proper state. Dmraid cannot boot from RAID Volume, OROM can boot from IMSM RAID Volume directly. You don't need separate partition, hard drive or anything else. If you run Intel platform you can boot directly from supported RAID Volume. This is because OROM supports it. Mdadm respects OROM restrictions when creating IMSM based RAIDs. Spanning in Linux is something obvious. I know that is simply works because of Linux architecture. However spanned RAID Volumes are not supported in OROM and in Windows. If you allowed for spanned RAID Volumes in Linux we open the Pandora's box. In the worst case you will lose you data when entering to OROM (OROM will see only one set of disks attached to one controller and can mark RAID Volume as Failed) or if you boot to Windows (Windows driver will see two failed RAID Volumes in the worst case). In other case you will have RAID Volume marked as Degraded and rebuild will start. And what if you create 'bootable' RAID Volume? Well you may not be able to boot from it when it's spanned. It's all about compatibility. Windows and OROM don't support spanned RAID Volumes so must Linux. Note that mdadm is not limited to IMSM metadata. You can use DDF or native metadata. It's just an option. But if you use IMSM metadata you are limited to Intel platform. I hope that I clarified a little bit. maciej > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v2.0.17 (MingW32) > Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ > > iQEcBAEBAgAGBQJQ9BnyAAoJEJrBOlT6nu75tikH/jQAsx4waselA6rrKC8aFD7+ > oG5pphTskS10iukkJGX8d+o/HiiMM66IuMqM3vRSNZO40P6arhAETE02jvNY9vFN > fI61AMpCv0FvBFv83RRmh19HkHLQEgiztcLRI7GeTNl5aOnC4wk8NY/Rqt022bhV > MGHickXUDNXtoWSXE3x03aXm9cwjIwfPbDrt3jOyrf9EqgZZW2j8uqY3PbH5Zcav > slKjFOaVt98nvLeDLpBJ6pR4vKq3Qax+pOPNdvlGG0GAqftH/iEYHsopmM4D4o5L > 21cI1CRfmyaF8ro0ryZPJkQVe46Ya41Qb1wd9Y6pg5mfbqGiwbQvMHi7o53Mc70= > =NumJ > -----END PGP SIGNATURE----- ��.n��������+%������w��{.n�����{����w��ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
