Linux-kernel mailing list archive 2000-06,: Re: Mirroring Root Disks

# Re: Mirroring Root Disks

Andre Hedrick (andre@suse.com)
Fri, 11 Feb 2000 22:11:55 -0800 (PST)

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You have made an eligant point; regardless, I do not do what you propose
because ATA ...... the kernel does not yet know how to fake the OS in
switch to get a boot in a failure.

I will trump the debate with a $2600.00 ATA-Hardware RAID solution I
showed at LWE@NYC.NY 2000.

$2600.00 == 320GB (8x40GB ATA Disks) and an 8-channel Host (3ware).
This was a RAID 0 stripe.

Imagine that you can remove the disks and shuffle in any order (on the
same card) and it finds-reconstructs the RAID?

SCSI can not touch 320GB in disks for $2600.00 USD.

On Fri, 11 Feb 2000, Martin Bene wrote:

> At 00:48 11.02.00 -0800, Andre Hedrick wrote:
>
> >> Is there a good way to mirror Root disks.
> >>
> >> Is RAID-1 only options for mirroring under Linux or something else is
> avialable.
> >> If RAID-1 is the only option, how safe, fault tolerant it is.
> >>
> >> I fear setting up RAID for root, as any problem with RAID may make
> system unbootable. Any
> >> comments. suggestions links on Root disks mirroing ????
>
> >Do hardware RAID..........ATA or SCSI but that is you only bet.
>
> Granted - Hardware Raid is probably the most stable and professional
> solutin - it's not the only one however:
>
> You CAN have software raid for every part of your disk, including /.
>
> A few pointers on software raid:
>
> * have a look at the howto on http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
> * You want to use the raid 0.90 code available as patches for 2.0 and 2.2
> kernels, not the code included in the kernel tree
> * With the 0.90 raid code, / on raid (any type - 0 / 1 / 4 / 5 work equaly
> well) is no problem, the raid arrays get initialized by the kernel on
> bootup and can be mounted just like any other device.
> * Swap on raid is currently problematical - I think background
> resynchronisation of mirror drives conflicts with use as swap; if you
> ensure that no resynchronisation takes place while the device is used as
> swap, it should work. Swap on raid would only make sense for mirror or
> raid5 to gain reliability.
>
> The only bit of configuration that's still a bit tricky is where to keep
> the stuff needed by the bootloader to get a kernel into memory; usually the
> stuff stored in /boot for lilo configurations. There are several ways of
> dealing with /boot stuff:
>
> * have a seperate non-mirrored /boot1, /boot2 etc. on each of the disks
> containing mirrors of your / filesystem, have lilo write startup info to
> each disk by having a seperate lilo.conf for each disk.
>
> * have /boot on a raid1 mirror and use a patched version of lilo (patch by
> redhat available in the redhat 6.1 source stuff). The patched lilo can
> handle raid1 mirror devices and will make each of the devices in a mirror
> bootable.
>
> As for stability: The linux raid 1/4/5 code can handle failing disks
> without requiring user interaction; you have to be careful with your setup
> however - some errors have to be avoided to allow continued operation in
> case of a drive failure:
>
> * Don't put two parts of a raid device on the same IDE bus (master/slave)-
> chances are that a failing master drive will take a slave on the same cable
> with it, causing two drives to fail at the same time -not good. Besides, it
> wont help performance either.
>
> * If you're using SCSI, be careful which controllers / drivers you use -
> some drivers don't handle failing disks well at all and will lock up your
> system or slow it to a crawl by stubbornly trying to access the dead disk
> and resetting the bus on failure indefinitely if a disk goes down.
>
> Bye, Martin
>
>
> "you have moved your mouse, please reboot to make this change take effect"
> --------------------------------------------------
> Martin Bene vox: +43-316-813824
> simon media fax: +43-316-813824-6
> Andreas-Hofer-Platz 9 e-mail: mb@sime.com
> 8010 Graz, Austria
> --------------------------------------------------
> finger mb@mail.sime.com for PGP public key
>

Andre Hedrick
The Linux ATA/IDE guy

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