Level 1 RAID: Software v. IDE Hardware on gentoo?

[idiotprogrammer]

Hi, I need to have RAID 1 on my two hard drive system. It will be for a home web server with a fair amount of traffic, databases and applications.

I've seen some good threads on RAID http://forums.gentoo.org/viewtopic.php? ... light=raid
and
http://forums.gentoo.org/viewtopic.php? ... =highpoint
and
http://forums.gentoo.org/viewtopic.php? ... light=raid

http://forums.gentoo.org/viewtopic.php? ... light=raid
http://forums.gentoo.org/viewtopic.php? ... light=raid

I gather that to set up HW Raid, you need a 1.2 CD to boot (1.4 doesn't boot off a CD to a RAID system for some reason).

I can spend $100-150 on a PCI IDE Raid controller, but some have talked about software RAID solutions. Also, I see the documentation about EVMS, which seems to have LVM capabilities. How well is hardware level one RAID (on IDE PCI) supported in linux/gentoo? Brands to avoid?

How much harder is software RAID to set up on gentoo? How much a drop on performance is there?

For a two disk RAID one system, would EVMS be overkill? Or would it make my life significantly easier?

Robert Nagle
www.idiotprogrammer.com

[DrSeltsam]

As far as i remember software raids are as fast as hardware raids but it costs a little bit cpu power. I am using a P4 2,4 GHz and there is no diffrence if i use a software raid or if i use a hardware raid. If you can live with 2 or 3 percent less cpu power you can save the money and use software raid.

[delta407]

I use (on a daily basis) both hardware and software RAID arrays. Software RAID is for most of my systems (the ones with >1 disk, at least) and performs up to my expectations. The hardware ones are on two servers I maintain because they're nice arrays -- you know, fibre channel host interface, twelve SCSI drives, hot spare with automatic reconstruction in the event of a downed drive, etc. Unfortunately, these kind of hardware RAID controllers run around $2000, which I don't want to spend on storage quite yet.

Software RAID also gives you flexibility. In a computer that I will shortly be installing 3 100 GB drives in, I will have three partitions -- the Gentoo standard /boot, swap, and /. The thing is that, unlike the hardware RAID controllers above, I can make /boot RAID 1, / RAID 5, and swap RAID 0. If I lose a drive, /boot and / are intact, and since the Linux IDE subsystem will force me to take the box down anyway, I can live without the swap partition.

Software RAID under Linux gives the best bang/buck ratio if you don't have obscenely high availability requirements. If your system goes down and people die as a result, go with hardware RAID. If your system goes down and you don't notice it's offline until a few hours go by, go with software RAID.

How much harder is software RAID to set up on gentoo?

In many cases, md is easier to configure than it is to get the kernel to see your IDE RAID controller.

How much a drop on performance is there?

Very little. Unless you have 150 MB/s disk writes on a Pentium 133, you'll be fine.

For a two disk RAID one system, would EVMS be overkill?

Very much so.

[rommel]

usr LSR and evms if you can , i have been running LSR since i started using linux/gentoo in april , i use raid0 but its been solid as a rock , i just added evms to a my new kernel (2.4.20) and switched to it from the md drivers in the kernel , its great

look into using evms and LSR would be my suggestion , if you wnat real hw raid i am afraid the cost will be more like 250 and up , and for that i think i would look at 3ware.

[idiotprogrammer]

Thanks for all the feedback. That makes me feel a little more confident about a software solution. Sourceforge mentioned that evms is still in alpha release. On a home production server, there seems to be risks associated with doing things the evms way. Is it very hard to change over to evms when it is more stable? Would running LVM for the time being prevent/make it difficult to transition to EVMS?

Rj

www.idiotprogrammer.com

[col]

The big advantage of using this:

http://forums.gentoo.org/viewtopic.php? ... =highpoint

- it is cheap & many motherboards already have the controllers

- you can hotswap drives with the correct drive bays

- if a drive dies there is no downtime

You may also be able to do a similar thing with the promise controllers using this partial open source driver:

http://www.promise.com/support/file/driver/2_relb25.tgz

[rommel]

hey idiot , i was using md from the kernel before i patched it with evms and all i did was recompile turning off the md stuff and enabling all the evms stuff , then i changed fstab to reflect the change to evms /dev/evms/md/md0 (where as before it eas /dev/md0) and changed grub the same way i.e. root=/dev/evms/md/md0.

that was all the switch needed to boot using evms instead of the kernel md driver.

faster too....as for alpha release , well thatsw kinda always the case except for debian maybe , but you could use 1.2.0....there is an issue in gentoo with the latest version , starting from the cli i get this error.

Code: Select all

EVMS Command Line Interpreter Version 1.2.0



Engine: The plug-in Ext2/3 in module /lib/evms/libe2fsim.1.2.1.so requires Engine services API version (8.1.0) which is greater than this Engine's services API version (8.0.0).




Engine: The plug-in failed to load.

but drobbins is aware of it and i am sure it will be fixed soon , /boot is the only thing that runs ext3 so i havent exerienced any trouble. evms itself though is a very nice disk managing tool above its ability to recognize and boot LSR....so keep looking into it.

ciao