[BozemanLUG] more RAID questions

[Brian Vincent]

I thought you could do it because you can boot from volume groups and the underlying RAID should be pretty transparent. However I'm probably finding the same documentation you've been looking at online and it seems like you have to boot from a single disk or RAID1.  I know back in the good ol' days it was definitely that way - you definitely couldn't boot from RAID5.  I thought all that changed when LVM came into play, but maybe not.

So... I forget why you didn't want to use LVM and I can't remember why you didn't want to use hardware RAID either (it's really the best way by far to do RAID.)  Scott mentioned a hardware card below, one thing to be very careful of is RAID cards that are proprietary and require a custom kernel driver to do the RAID.  Almost none of them used to work with Linux, but I bet some of them have drivers now.  

Anyway, this link makes it pretty clear you can't do it:
http://www.linuxquestions.org/questions/linux-software-2/can-boot-be-on-a-software-raid5-array-648567/

So, my recommendation would be to throw another disk in the system for your /boot just to get it configured and running.  Then, copy your /boot to a USB key or CD-R or something and have your BIOS boot from that.   Don't forget to make a backup of your USB key or CD-R.

-----------------------------
Brian Vincent
Moonlight Basin Technology
bvincent at moonlightbasin.com

-----Original Message-----
From: discuss-bounces at bozemanlug.org [mailto:discuss-bounces at bozemanlug.org] On Behalf Of Scott Dowdle
Sent: Thursday, October 14, 2010 11:44 AM
To: rpotter at zoncko.com; Bozeman Linux Users Group
Subject: Re: [BozemanLUG] more RAID questions

Rob,

----- Original Message -----
> OK, I have some more questions. All the instructions I find on line
> always tell you the instructions will work for all RAID's but then
> they only use RAID 1 as the base for the instructions.
> 
> As I studied my space needs, I decided I needed to maximize.
> Originally I was going to stripe two sets of 1 TB drives and then RAID 1 the two
> striped sets. But this would only give me 2 TB of storage. Nothing to
> sneeze at, but at first glance RAID 5 would give me 3 TB (4 x 1 TB).
> 
> So I started following the instructions which is when I think I hit a
> snag. the instructions have you create a new partition - the first of
> which is the SWAP. Then the next partition is set as boot-able and ext
> 4 file system. This configuration makes perfect since if using RAID 0
> or 1, but from what I can tell this won't work for RAID 5.
> 
> I have also seen some indication in the instructions I have found that
> say boot-able cannot be RAID 5. Some say you cannot have RAID 5 OS but
> others imply that you can.
> 
> So my first question is can I have the OS, SWAP, and data storage
> under RAID 5? If so, how do I configure this? With RAID 1 I would duplicate
> the SWAP and boot-able partition but that does not make sense under
> RAID 5.
> 
> This server box can hold 4 drives and each drive is only allowed to be
> no bigger than 1 TB in size. So, setting up a solo drive for the OS
> will cost me drive space and will prevent redundancy of the installed
> OS. If I have two drives dedicated to the OS running RAID 1 then I
> lose even more needed space.
> 
> So the way I look at it, either I am missing something for setting up
> RAID 5, or my only option for redundancy and max space is stripping
> two sets of two 1TB drives then mirroring the two sets. Is this my only
> option?

I read all of that and I understand what you are asking.  I just don't know the answer at the moment as I've only time I've used Linux software RAID it was with RAID 1.

Question:  Please state the make and model of the server.  If it is a Dell box, you can get a hardware RAID card that is Linux compatible for $175 (or at least I did recently for a Dell PowerEdge R510 server with SAS drives).  I know you can use RAID 5 with that and the OS just sees it as one big drive.

You have previously stated you didn't want to go that route... so I'll investigate some and see if I can find you an answer.

TYL,
-- 
Scott Dowdle
704 Church Street
Belgrade, MT 59714
(406)388-0827 [home]
(406)994-3931 [work]
_______________________________________________
Discuss mailing list
Discuss at bozemanlug.org
http://lists.bozemanlug.org/mailman/listinfo/discuss