[sclug] Raiding partitions

Sun Apr 10 18:13:05 UTC 2005

Thanks for all the advice, everyone who leapt to help.

I'm not really fussed about mirroring or syncing from Windows. I only 
use WinXP for Quicken (for historical reasons), and although given the 
choice my wife prefers it (safety in familiarity and all that - she's 
comfortable with it from use at work) she's not a big computer person,  
so Windows really doesn't get used a lot and I just want to ensure that 
the Windows data is protected in some way. The ideal compromise for me I 
think will be to mirror the two data partitions (Win D: and /home) from 
within Linux. Alternatively rsync sounds interesting  (frankly my data 
doesn't change a huge amount week to week anyway so a daily rsync job on 
boot or shutdown will not be too onerous, I guess). I'll give it a whirl 
and let y'all know how I get on. :-)

BTW I'm using a new Maxtor DiamondMax drive now as my main drive, and a 
1 yr old Seagate Barracuda as the spare 'backup' drive. The Seagate is a 
mile quieter than the Maxtor, which itself is pretty quiet (in case 
anyone is interested).

Thanks everyone for the prompt help.

Regards,

Neil.

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>------------------------------------------------------------------------
>
>Today's Topics:
>
>   1. Raiding partitions (Neil Haughton)
>   2. Re: Raiding partitions (Matt)
>   3. Re: Raiding partitions (Keith Edmunds)
>   4. Re: Raiding partitions (John Stumbles)
>   5. Re: Raiding partitions (Alex Butcher)
>  
>
>
> ------------------------------------------------------------------------
>
> Subject:
> [sclug] Raiding partitions
> From:
> Neil Haughton <n.a.haughton at bigfoot.com>
> Date:
> Sat, 09 Apr 2005 13:47:24 +0100
> To:
> sclug at sclug.org.uk
>
> To:
> sclug at sclug.org.uk
>
>
> Can anyone help me with some advice?
>
> Following a yet another hard drive disaster (head crash) I'm doing 
> something to prevent the anguish  from re-occurring. Can anyone advise 
> me what I need to do to set up partition-partition mirroring?
>
> I have two drives now, an 80G drive ADA-133 (/dev/hda) which has a 40G 
> partition for my home partition, and a 40G ATA-100 drive (/dev/hdc), 
> which I want to use as a mirror for the home partition on hda. I'm not 
> bothered about mirroring the other 40Gb 'system and apps' partition.
>
> Can this done with an IDE PCI RAID card (I've seen a cheap PCI IFDE 
> RAID card in Maplins), or is it best done using software RAID?
>
> BTW I'm using Mandrake 10.0 and WinXP Pro (dual boot), so my 40G 
> 'home' partitions are each really two partitions, a 20G Linux /home 
> and a 20G Windows 'drive D:'. I was hoping to get both pairs of 
> partitions to be synchronised when I run Linux (which is most of the 
> time).
>
> Is this the right approach, and how should I proceed? Any pitfalls to 
> look out for?
>
> BTW If you get the temptation to buy an IBM/Hitachi DeskStar drive, 
> don't. I've twice in succession had mine fail under warranty within 2 
> years. Must be the most unreliable drives I've ever come across.
>
> Regards,
>
> Neil Haughton
>
>
> ------------------------------------------------------------------------
>
> Subject:
> Re: [sclug] Raiding partitions
> From:
> Matt <matt at bodgit-n-scarper.com>
> Date:
> Sat, 09 Apr 2005 14:49:20 +0100
> To:
> sclug at sclug.org.uk
>
> To:
> sclug at sclug.org.uk
>
>
>This probably rules out using software RAID 100% then, as Windows
>wouldn't be able to access the software RAID that Linux created, and
>(assuming Windows has software RAID) vice versa. They tend to be
>OS-specific.
>
>Cheap IDE PCI RAID cards are not real RAID cards, as a proper one
>handles all of the RAID functionality and just presents the
>mirrored/striped/... volume to the system which to all intents looks
>like a regular disk. These cheaper ones require the OS to do some of the
>RAID function which means you need both of your OS' to be able to drive
>your card as a RAID card. Linux tends to just use these as extra IDE
>controllers, although I think it can work with certain models. Also, I
>don't know of (m)any RAID controllers that can mirror just a single
>partition, they tend to deal only with whole disks.
>
>Alternatively, you can do your own pretend mirroring under Linux using a
>cron-driven script to use something like rsync to periodically copy the
>data, using a frequency of your own choosing. Downsides are running this
>too frequently will create extra load on your machine, and too long a
>period and you have the potential to lose data.
>
>  
>
>You could use software RAID for your Linux /home partition and a cron
>job to backup your Windows partition. If you don't access/modify your
>Windows data under Linux, then you can simply perform this once when
>booting into Linux.
>  
>
>HTH
>
>Matt
>
>  
>
>
> ------------------------------------------------------------------------
>
> Subject:
> Re: [sclug] Raiding partitions
> From:
> Keith Edmunds <keith at midnighthax.com>
> Date:
> Sat, 9 Apr 2005 16:18:04 +0100
> To:
> sclug at sclug.org.uk
>
> To:
> sclug at sclug.org.uk
>
>
>On Sat, 09 Apr 2005 13:47:24 +0100
>  
>
>It can be done with a RAID card, but I wouldn't. The problem is that most
>RAID cards store the data in a proprietary format on disk, so if/when your
>RAID card breaks you are left with just your backups. Mirroring in the
>Linux kernel is very efficient and just works. That's what we do with just
>about every server we build. You can remove one disk of a Linux mirror
>pair, put it in another system and boot it - no proprietary formats in
>sight.
>  
>
>This won't work with Windows. There's a software RAID howto which should be
>Google-able. If you're only wanting to mirror data (as opposed to boot from
>a RAID set) then it's pretty straightforward to do. Booting from RAID isn't
>that hard, but it is a little more tricky.
>  
>
>We've had very poor experiences with IBM disks. That said, for any
>manufacturer you'll find someone who has had a bad experience. FWIW we use
>Maxtor disks now, which has worked out pretty well (so far!).
>
>Keith
>
>  
>
>
> ------------------------------------------------------------------------
>
> Subject:
> Re: [sclug] Raiding partitions
> From:
> John Stumbles <john at stumbles.org.uk>
> Date:
> Sat, 09 Apr 2005 18:50:38 +0100
> To:
> sclug at sclug.org.uk
>
> To:
> sclug at sclug.org.uk
>
>
>
> If the aim is to ease the pain of recovery after the occasional disk 
> crash rather than acheive 24/7 availability then automated backup to 
> another filesystem would seem satisfactory. If you add automatic 
> archiving to the backup system and from that to tape/dvd then you have 
> the advantage of being able to recover from certain instances of 
> finger trouble and other nasties that raid doesn't do for you.
>
> Sadly my homebrew system for doing this is still lacking a few Tuits, 
> and I don't know of any such systems available Out There (tm)
>
>
>
> ------------------------------------------------------------------------
>
> Subject:
> Re: [sclug] Raiding partitions
> From:
> Alex Butcher <lug at assursys.co.uk>
> Date:
> Sat, 9 Apr 2005 21:26:52 +0100 (BST)
>
> CC:
> sclug at sclug.org.uk
>
>
>
> The Promise RAID solutions only work on a whole-drive basis. I expect 
> that
> this will be the same for competing manufacturers' cards.
>
>
> Well, as Matt said, the cheap RAID cards are effectively software RAID
> anyway (the RAIDing is done in the OS driver). Again, as Matt said, 
> Linux's
> software RAID can't be accessed by Windows, and I don't think Windows' 
> RAID
> is readable by Linux (though this will probably be what happens first 
> out of
> the two!). Furthermore, Linux's software RAID requires you to encapsulate
> your partitions inside a special RAID partition type, so you'd need to
> backup your data, re-partition both drives, RAID them, then restore the
> data. If you don't want to do that...
>
> ...then I'd suggest having a script which unmounts the partitions and 
> uses
> dd to copy one to the other. You'll need to make sure that your 40G 
> drive is
> actually slightly larger than the two 20G partitions.
>
>
> Promise have drivers to allow their RAID format to work with Linux, but
> IMHO, it's not worth the hassle - it forces you to stick to certain 
> kernel
> binaries, is less portable, and offers no performance gains. The only 
> reason
> to use it, IMHO, is if you have a pre-existing Promise RAID setup 
> which you
> wish to continue to use, or migrate data from.

>
> IMHO, the best approach at this sort of budget is to buy two equally 
> sized
> discs and use each OS's native software RAID. The downside is the money
> required to do that. :-/