software RAID-0 recommendations

[Alexander Dalloz]

Am Di, den 07.09.2004 schrieb Christopher J. Bottaro um 17:18:

> i just bought a motherboard with onboard SATA RAID and two SATA hard drives
> for my linux box before i realized that you can't utilize the onboard RAID
> controller when installing linux.  so i'm left with linux's software RAID
> option.  i've seen two software RAID setups and i'd like to ask your
> opinion on them:

Linux software RAID is no disadvantage, given you have not the money to
spent into a read hardware RAID controller like those by 3ware or ICP
Vortex (now Intel company and leaders with SCSI RAID controllers).

> given identical hard drives: /dev/sd0 and /dev/sd1
> 
> first method:
> * create swap partition on /dev/sd0
> * create boot partition of exactly the same size as the swap on /dev/sd1
> * create a software RAID partition on both /dev/sd0 and /dev/sd1 taking up
> the remainder of the drives
> * create a RAID-0 device using those two software RAID partitions without
> mount point /

I do not understand the last step: what means "without mount point /"?
From what you intend I would mean the main space on both drives is a
RAID0 array with / on it, excluding /boot and swap.

Btw. you can use more than 1 swap partition. If giving them same
priority then they act comparable to an interleaving RAID.

> second method:
> * create /boot partition on /dev/sd0
> * create /dummy partition on /dev/sd1 that is exactly the same size as /boot
> * create a software RAID partition on both /dev/sd0 and /dev/sd1 taking up
> the remainder of the drives
> * create an LVM device using the two RAID partitions
> * create swap and / on the LVM

Besides having /boot on a third drive and swap not on LVM, I have a
similar setup, using LVM.

> the first method is simpler, but has the disadvantages of having a
> needlessly large /boot partition and also not having swap on the RAID.  are
> there any disadvantages to doing it the LVM way?  am i even using the LVM
> correctly in the second method?  hell i don't even really know what an LVM
> is, all i know is that it allows me to make multiple partitions on a
> software RAID-0 device.

In the first scenario you could create small partitions of equal small
size (>=76 MB) and use one of them for /boot. Create on both disks too 2
partitions for swap. If you intend to use 512 Mb swap space both
partitions can be each 256 MB large.

Using LVM you should know what it is and how to handle it - if you call
it a disadvantage.

http://www.redhat.com/docs/manuals/enterprise/RHEL-3-Manual/admin-guide/s1-storage-adv.html#S2-STORAGE-ADV-LVM
http://www.redhat.com/docs/manuals/enterprise/RHEL-3-Manual/sysadmin-guide/ch-lvm-intro.html
http://www.redhat.com/docs/manuals/enterprise/RHEL-3-Manual/sysadmin-guide/ch-lvm.html

LVM offers the big advantage that you can easily extend the space if
getting low free space.

Btw. neither RAID nor LVM do make backups useless. Especially
considering RAID0 arrays raises the risk of data loss when one array
element fails.

Alexander


-- 
Alexander Dalloz | Enger, Germany | GPG key 1024D/ED695653 1999-07-13
Fedora GNU/Linux Core 2 (Tettnang) kernel 2.6.8-1.521smp 
Serendipity 18:23:10 up 8 days, 15:39, load average: 0.30, 0.21, 0.26 
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