From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: raid0 not growable? Date: Thu, 24 Dec 2009 10:54:24 +1100 Message-ID: <20091224105424.62c41b25@notabene> References: <73e903670912230552n226e9052q182174cba32f3c54@mail.gmail.com> <20091224094557.1ae96a0d@notabene> <73e903670912231528u6d3cd2ekd0fa4ade06adbcf5@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <73e903670912231528u6d3cd2ekd0fa4ade06adbcf5@mail.gmail.com> Sender: linux-raid-owner@vger.kernel.org To: Kristleifur =?UTF-8?B?RGHDsGFzb24=?= Cc: linux-raid List-Id: linux-raid.ids On Wed, 23 Dec 2009 23:28:37 +0000 Kristleifur Da=C3=B0ason wrote: > On Wed, Dec 23, 2009 at 10:45 PM, Neil Brown wrote: > > On Wed, 23 Dec 2009 13:52:54 +0000 > > Kristleifur Da=C3=B0ason wrote: > > > >> Hi, > >> > >> I'm running a raid0 array over a couple of raid6 arrays. I had pla= nned > >> on growing the arrays in time, and now turns out to be the time. > >> > >> To my chagrin, searches indicate that raid0 isn't growable. Can an= yone > >> confirm this before I wipe and reconfigure? > > > > That is correct, you cannot currently grow md/raid0. > > > > If the two raid6 arrays are exactly the same size, then you > > could grow the two raid6 arrays, create a new raid0 over them > > with the same block size and all your data will still be there. > > But if they are not the same size, that won't work. > > > > NeilBrown > > >=20 > Many thanks for the reply. (Re-cc'd to the linux-raid list. Hope that= 's OK.) Certainly. I didn't mean to drop linux-raid - I must have clicked the = wrong button. >=20 > 1. > The raid6 arrays are exactly alike. Do I just do a create a new raid0 > with the right size, device count and chunk-size parameters? I trust > your advice, but I am also certain of my own foolishness. I can't > fully picture what happens to the data on the array -- Specifically, > I'm thinking about whether to use --assume-clean or not. The > documentation says not. I am guessing that a newly-created raid0 > doesn't do any syncing/resyncing anyway - it just sets up the array > structure and metadata and I am left to my own devices to fill it wit= h > data. >=20 > Current chunksize is 256 and metadata is 1.1. So it's just a "mdadm > --create /dev/md_bigraid0 --level=3D0 --raid-devices=3D2 --metadata=3D= 1.1 > --chunksize=3D256 /dev/md_raid6a /dev/md_raid6b", right? Yes... there is a possible complication though. With 1.1 metadata mdadm reserves some space between the end of the meta= data and the start of the data for a bitmap - even for raid0 which cannot ha= ve a bitmap. The amount of space reserved is affected by the size of the devices. So it is possible that the "data offset" will be different. You should check the data offset before and after. If it is different,= we will have to hack mdadm to allow you to set the data offset manually. >=20 > 2. > I have a JFS filesystem on the big raid0. Once I have the bigger raid= 0 > built, I assume that I would first do a read-only fsck.jfs, which wil= l > succeed if I did everything correctly. Then I do a remount with the > "resize" option to JFS to finally grow the JFS filesystem. Sounds right (though I've never used jfs). >=20 > -- >=20 > Sincere thanks. I hope I shall be able to contribute something > meaningful to mdadm when the company is richer and my time is freer := ) > In the meantime, is there any preferred way of donating to mdadm or > sponsoring it? > Just use it and report any issues you have, as you have done. NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html