Topic: RAID 5 vs. RAID 1 in SME 7.x?

[djhomeless]

Hi All,
Not really looking to ask the differences between the two types of RAID in a general sense, more as it pertains to SME 7.

My old server died on went to heaven so I'm rebuilding the box from scratch. I've got 3x 160 gig drives, and a RAID controller that is capable of handling RAID 0, 1, 5, and 10. I'm leaning towards RAID 5 so I can get the redundancy without losing the space like I would with RAID 1.

Do you guys have any personal preference for your boxes? My SME is fairly typical, its a File and Webserver, but mostly web & email.

Any advice would be appreciated.

Thanks,

Geoffrey

[djhomeless]

This post is rather interesting:

http://forums.contribs.org/index.php?topic=26762.msg118861#msg118861

Can I assume that by using the software RAID, I can avoid the whole trouble of compiling my RAID controller's drivers, which would have been combersome at best?

So, I still use the controller to link up the disks, but leave the physical RAID management to SME?

[MSmith]

Looks as though 7.0 is just helluva smart about RAID ... so throw that CD in there and see what happens, then let us know!  Especially make & model of controller, etc.

[raem]

djhomeless

> So, I still use the controller to link up the
> disks, but leave the physical RAID management to SME?


If you use a hardware RAID card then in sme server initial installation you just select single disk.
The RAID functions are performed by the card so the server effectively just sees a "single" drive.


If you remove the hardware RAID card, then you attach a drive to channel 1 and channel 2 on your motherboard, and select software RAID1 in sme server initial installation.
sme server then takes care of the RAID1 functions.

Either software RAID1 or hardware RAID10 will give you the safest server.

Just use 2 drives for software RAID1 to give you data redundancy.

You really need 4 drives for RAID10 using the hardware RAID card.

Personally I would just configure your server with 2 drives in software RAID1 (without a RAID card) and then use your third hard disk as a removable RAID member. You periodically remove a drive and rebuild the array with your third spare drive. That way you have a fully configured server backed up on disk. If your whole server ever fails you can be up and running a fully configured system relatively easily with the single spare drive in degraded software RAID1. All you need to do is replace the data with the most recent from the normal daily backup.

[raem]

djhomeless

> Not really looking to ask the differences between > the two types of RAID in a general sense, more as it pertains to SME 7.


This devinfo post explains the capabilities of sme 7 wrt RAID & number of disks installed.

http://lists.contribs.org/mailman/public/devinfo/msg08317.html

It says (in part)

- Automated installation as RAID
 - 1 disk: One-way RAID1 mirror
 - 2 disks: Two-way RAID1 mirror
 - 3-5 disks: RAID5
 - 6+ disks: RAID6

[Reinhold]

FWIW,

I have done installations with 3 and 8 disks with SME7 betas (latest b8).

RAIDx doesn't get any simpler/better than SME7 !!!


Exception: (IMO) Software Raid6 isn't quite ready  
- too slow too wasteful in our Small&Medium regime(again IMO).
Consequently I modified smeinstallclass.py back to max Raid5 and burned a new (7b8) install CD.

RAID5 works with heavy load (video) for demanding customers (school/non_profit_"kiddies"   ).

For any new SME7 server I'd use 2HD software Raid1 _or_ software Raid5.
I will not buy any Hardware incl. 3ware in the forseeable future.
I'd think "SmallMedium"E  is "dead territory" for HW Raid
...buy a faster cpu, more RAM and more disks for your money .

Regards
Reinhold  

BTW: RHEL/Centos/SME lvm is/works great !

[Reinhold]

BTW  Ray,Geoffrey,

I do not see any reason not to install all three of djhomeless's disks as a software Raid5.

(3-1)x 160Gb=320GB vs just 160GB and as icing a slightly faster disk configuration are reason enough for me...

Just plug them in "and say YES" when (not) asked


Regards
Reinhold

[djhomeless]

Don't I feel foolish. I bought a Highgate RAID card thinking it was the only way to get a flawless RAID 1 or 5....now it seems I could do it just by hooking my 3 disks up to my board as normal.

I'm still leaning towards RAID5 simply because I'd like to start using more video and audio in my LAN (ok, my house).

It seems a lot of people are saying SW RAID is just as good as HW, but I thought the whole point of the controller was to help maximise throughput and such.

Heck, I'm not complaining. The card was £110, so I could easily return it for more server swag.

Thanks Everyone!

Geoffrey

[Alex Schaft]

Hi,

I'm currently not very familiar with RAID, but was just curious on how hardware and software RAID compare when a drive fails, as well as the power. Would both be able to boot the server from the raid with a failed drive?

Alex

[jphilip]

Hi,

I'm currently not very familiar with RAID, but was just curious on how hardware and software RAID compare when a drive fails, as well as the power. Would both be able to boot the server from the raid with a failed drive?

Alex

With two IDE drives I installed 7b8 and it automatically set up raid. Copied some files across to the server, shut it down and disconnected either drive and it boots and runs as normal.

What I cannot find is any instructions on how to rebuild the raid after replacing a drive. Pointer anyone ?

[Reinhold]

folks,


Read:
- Software-RAID-HOWTO
- Managing RAID on Linux
- search in contribs. There are many many threads on this stuff .-)
- subscribe to the linux-raid mailing list, hosted on vger.kernel.org

...for SME7 you will need to know about mdadm too. Start biting into man mdadm then look here

As to software vs hardware raid (from Derek Vadala as shown above):

Software RAID has unfortunately fallen victim to a FUD (fear, uncertainty, doubt)
campaign in the system administrator community. I can’t count the number of system
administrators whom I’ve heard completely disparage all forms of software
RAID, irrespective of platform. Many of these same people have admittedly not used
software RAID in several years, if at all.

And Valada's book is 2002.
In 2005, in the age of 3GHz+ CPUs, I (personally) find little value in hardware raid for the SM-E domain we are in.
Slow(er), inflexible, needs hardware backup (spare board), needs driver support and often isnt easily fixed by admin. - Oh yes EXPENSIVE too!


Regards
Reinhold
P.S.: Highpoint isn't even hardware raid. It's a bios chip, sometimes a tiny parity engine (mostly unused in Linux) and the SAME CPU ... iow software raid ... just in a proprietary way (duh).