Opinions on linux software RAID 5? ...and question about moving raid...

[BrettG]

First question... can a software raid 5 setup on a linux box be moved to another system? That seems kind of silly, sure... but I'm just looking at my expansion options and failover options.

Now for the opinion part...

On my home network, I'm doing much consolidation after years of a 'bigger is better' approach. My old 'dedicated file server' consisted of a 600GB raid on a promise SX6000 and RH9... ran well for more than two years ... That system is being replaced by an HTPC system that will double as the file server. Its running Mandrake 10.1 and currently the main file storage is on two 250 WD drives in RAID 1. I'd like to snag two more 250 GB drives and set it up as RAID 5.

This will be serving videos/music and important docs to a few machines, so performance isn't the biggest concern ... my next concerns are price, ease, and reliability. I know I could get a RAID 5 capable controller for ~$200, but then I'd have to deal with limited linux support and I don't really feel like futzing around with the system for days to get it up and running. I just want to plug each drive into a channel on the two Promise TX2-100 cards I already have and wrap them all up with the linuxraid using webmin. Any thoughts or experiences with something similar? Thanks!

 

[Tink]

Using software raid is just asking for trouble, no matter the OS vendor. Go with a hardware solution if you value your data at all. you can get a quality raid controller for less than a drive costs.

 

[BrettG]

Thanks for the response


Newegg has the 250gb drive for under $150 ... if you know of a raid 5 capable controller with mandrake support for that price...please point me to it! I can only find them in the low 200 range and I'd have to go suse or redhat in order to use their precompiled drivers.

 

[Tink]

Judging from this

http://www.mandrakelinux.com/en/hardware.php3

plugging in version 10.1 and raid controller i came up with this list. I would use this list and newegg\e-bay\[H] forsale forum\etc and make that raid array your bitch.

I realize not all of these are Raid 5 compatible and only a few are SATA but this is the raid controller list that is know working.

You were correct in your inital statement that finding a RAID 5 controller with support for Mandrake would be ~200$ new, if you really wanna do RAID 5 i would watch ebay for one that will work in your system.

[RAID adapter] ADAPTEC 1210SA (Mandrakelinux 10.1, x86) Compatible
[RAID adapter] ADAPTEC 2410SA (Mandrakelinux 10.1, x86) Compatible
[RAID adapter] ADAPTEC 2810SA (Mandrakelinux 10.1, x86) Compatible
[RAID adapter] ADAPTEC 7901A-HostRaid (Mandrakelinux 10.1, x86) Compatible
[RAID adapter] AMERICAN MEGATREND MegaRAID IDE 100 (Mandrakelinux 10.1, x86) Compatible
[RAID adapter] COMPAQ LSI/SYMBIOS 53C895 (Mandrakelinux 10.1, x86) Compatible
[RAID adapter] COMPAQ Smart Array 5i/532 (Mandrakelinux 10.1, x86) Compatible
[RAID adapter] LSI LOGIC PowerEdge Raid Controller 4/QC (Mandrakelinux 10.1, x86) Compatible
[RAID adapter] LSI LOGIC PowerEdge Raid Controller 4/QC (Mandrakelinux 10.1, x86) Compatible
[RAID adapter] PROMISE PDC2037A (Mandrakelinux 10.1, x86) Compatible
[RAID adapter] QLOGIC series 475 (Mandrakelinux 10.1, x86) Compatible
[RAID adapter] SILICON IMAGE 3112A (Mandrakelinux 10.1, x86) Compatible

 

[nick58b]

I've run a software raid 5 array for ~6 months now (5x 120GB WD Caviar SE drives) on linux with no issues at all. I use it daily for serving videos/music to all my computers, and get decent performance (hdparm of 65 MB/s w/15% AXP2100+ cpu usage, enough to easily saturate my 100mbit network). As for your question, yes, you can move a software raid array from one machine to another. See here: http://howtos.linux.com/howtos/Software-RAID-0.4x-HOWTO-8.shtml

#12 Q: When is Software RAID superior to Hardware RAID?

A: Normally, Hardware RAID is considered superior to Software RAID, because hardware controllers often have a large cache, and can do a better job of scheduling operations in parallel. However, integrated Software RAID can (and does) gain certain advantages from being close to the operating system.

For example, ... ummm. Opaque description of caching of reconstructed blocks in buffer cache elided ...

On a dual PPro SMP system, it has been reported that Software-RAID performance exceeds the performance of a well-known hardware-RAID board vendor by a factor of 2 to 5.

Software RAID is also a very interesting option for high-availability redundant server systems. In such a configuration, two CPU's are attached to one set or SCSI disks. If one server crashes or fails to respond, then the other server can mdadd, mdrun and mount the software RAID array, and take over operations. This sort of dual-ended operation is not always possible with many hardware RAID controllers, because of the state configuration that the hardware controllers maintain.

The mdadd, mdrun, and mount commands would be what you need to bring the array up on another machine. Just be sure to copy the settings and get the drive order correct in your /etc/raidtab (or webmin, but I don't have any experience with that).

 

[unhappy_mage]

Software raid is really nice. It's the only RAID format that I can think of where if your controller dies you can move it to another machine with guaranteed success.

I run a raid-0 array which I will be breaking as soon as possible to move to raid-1. I have had a 5-disk array on 20MB/s SCSI which pushed the limits of the controller (16MB/s reads and writes), even though 1 disk only wrote at 7MB/s. These were old disks, and performance out of them was still decent.

My suggestion is, buy the disks, try the raid-5 in software, then decide if you need the hardware raid capabilities. Then buy a 3ware card if necessary.

 

[Tink]

For those of you running Software RAID 5, have you had a drive fail yet? If so how hard was it to rebuild your raid set and how long did it take? From my experience with RAID controllers, on Compaq, DEC Alpha and HP servers and mini's you replace the drive and the tools that you get with your raid controller rebuilds the set for you in an hour or so depending on how fast your drives are, controller cache size, and the size of your array.

As for losing a Controller, I have never had a problem powering down the machine, swapping in a new controller (same model) or moving an external cabinet to a backup machine with the same controller and just turning the machine on and it works, wait for your RMA part to come back and then replace the card and move the external cabinet back or if the server has the same specs as your backup, the one with the replacement card would turn into the backup at that point.

Software RAID may be the way to go for this person, that is a decision s\he is going to have to make for themselves.