From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lapohos Tibor Subject: Re: embedding area is unusually small... (GRUB2 on software RAID1) Date: Wed, 6 Jan 2010 13:40:46 -0800 (PST) Message-ID: <932657.98441.qm@web88207.mail.re2.yahoo.com> References: <1262825627.g6ATheBPQY@rnqqfki.eternal-september.org> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <1262825627.g6ATheBPQY@rnqqfki.eternal-september.org> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Thank you Antonio! --- On Wed, 1/6/10, Antonio Perez wrote: > However, you did repartition md0, while still expecting to > boot from md0. >=20 > That is "odd" to me. Just make a FS in md0 and use it as> > /boot (and root). I've been, and still am, puzzled by the efficiency of the calculations = involved in setting up RAID, one way or the other. And what I refer to,= goes down to number of clocks needed to perform the writing. As I was = wondering down this path, I figured that the way I set it up would be t= he most efficient. Of course, I do not know enough about the actual ker= nel/raid code to be able to tell for sure. My intuition dictated it thi= s way. > > should I create all the partitions first and build > > them into so many /dev/md[01234] devices separately maybe? > > I could tell you what seems to be a reasonable setup IMO: > =A0=A0=A0 200Mb --> {sda1,sdb1} --> md1 --> RAID1 --> use as /boot > =A0=A0=A0 5Gb=A0=A0=A0--> {sda2,sdb2} --> md2 --> RAID1 --> use as / > =A0=A0=A0 ... =2E...and that's exactly what is also on my list, and your suggestion e= nforces my thoughts, thanks. Nevertheless, it still does not explain to= me whether multiple md devices with more underlying disk partitions or= more md partitions with fewer underlying disk partitions are the way t= o go. To be absolutely clear, is the /dev/sd[ab]1 =3D> /dev/md0 =3D> /dev/md0p[123...] [RAID1] /dev/sd[ab]2 =3D> /dev/md1 =3D> /dev/md1p[123...] [RAID0] or the /dev/sd[ab][123...] =3D> /dev/md[012...] [RAID1,RAID0] setup the most stable, efficient and robust solution? The way I see it,= there shall be a difference somewhere, somehow, right? About the first= one, thanks to Michael E. pointing it out, we already know that one ha= s to take care about choosing the patritions. =46urthermore, I think that the gain in speed of RAID0 would start vani= shing if disk access is required on the RAID1 side all at the same time= =2E In fact, the whole system's efficiency would degrade. The only way = out would be to use 4 disks as /dev/sd[ab]1 =3D> /dev/md0 =3D> /dev/md0p[123...] [RAID1] /dev/sd[cd]1 =3D> /dev/md1 =3D> /dev/md1p[123...] [RAID0] Right? Keep in mind that I am not after what RAID10 can offer. I can af= ford giving up the data safety on the RAID0 side in exchange for speed. > Having only two disks means to use only RAID1. RAID0 is too > risky IMO as any disk failure means a complete loss of data. I will be developing a numerical electromagnetics code, that will do qu= ite some number crunching and dumping with 4xTesla C1060 GPUs. I will n= eed the RAID0 for that purpose, for a scratch space, if you will. So it= is a must have for me. > I am a common user which is trying to help you. Thanks, it's highly appreciated. > But, in this list alone, there are three post from you with exactly t= he > same content and question.=20 That's really odd. I would never do that intentionally. As I wrote earl= ier, I did submit it to 3 lists, help-grub, grub-devel and linux-raid, = but not to the same one 3 times. The subject is related to both RAID an= d GRUB, which is why I sent it 3 ways. My apologies again to all those = who got it in 3 copies, whether by being subscribed to all 3 lists, or = by a misterious triple submission of mine.=20 > If you are not getting any feedback, perhaps you should re-think=20 > of a different way to make your questions. And, please, > allow more time for an answer. I am a patient man, so not getting answers would not drive me to re-pos= t the same message again. > Thanks for your cooperation. Absolutely. And I thank to all for your help. All the best, Tibor -- 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