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bskrakes 07-02-2008 10:07 AM

Hardware RAID vs Software RAID and DATA RECOVERY
 
Hello all! So I have been going back and forth between setups for my home web server and file server. I used to have 2x 160GB hard drives in software RAID 1 and a single 500GB hard drive for storage. I recently purchased 3 more 500GB hard drives and swapped out the 2x 160GB with the new 500GB's.... Over the weekend and Canada Day I loaded Cent OS 5.0 with two pairs of the 500GB's in software RAID 1....

Here are my questions:

1) Which type of RAID should I use, hardware or software?

2) Is hardware RAID faster (I would assume so but only if you have the right hardware - my home computer is not a power edge dell)

3) How do I recover if the hardware or software RAID fails. I do believe that if you were running hardware raid and the motherboards on-board controller fails you would have to replace the board with the exact same board and controller. If you were using software raid and it fails can I just pull the drive and plug it in like an external drive to retrieve data? Or how do I recover from a failure with software raid?

4) Is there an OS version of Linux that performs better than another at using software RAID?

System Specs:
ASUS P5DL2-VM
Pentium D805 2.66Mhz 2MB Cache
EVGA e-GeForce 7200 GS
3GB DDR2
2x 1GB DDR2 Kingston Dual channel
2x 512MB DDR2 Mushkin Dual channel
5x 500GB Segate SATA HD (2 pairs in software RAID 1)
Pioneer DVR-110
Antec Sonata 2 w/450 watt PSU

So a basic system but a pretty sweet home server I think. It is also worth noting that I run VMware Server which hosts another Cent OS 5.0 for my web hosting I do on the side. Any advice would be great!

Thank you

mostlyharmless 07-02-2008 11:27 AM

Like the "which distro is best" question, there's is probably no single answer.
This is a good place to start:
http://en.wikipedia.org/wiki/Redunda...ependent_disks
which you've probably read.

As for recovery; RAID is not backup; I recommend backup to a bare metal recovery alternate disk, with at least one disk on an off site rotation.

Hotswapping is supported only by certain hardware - doesn't sound like your situation would be included.

so..
(1) can't answer
(2) true hardware raid, higher end, is probably faster
(3) bare metal backup
(4) not that I know of

bskrakes 07-02-2008 01:03 PM

Ok to your point of off site backup, I do have a second network storage device that I am backing up to. So what I have in my network is the one file and web server running a RAID array for extra redundancy but am also doing daily/nightly backups to a network storage device.... So I do have true redundancy. The only downtime I would experience is the time to rebuild the OS... however I have an old AMD Athlon/Duron machine sitting there ready to go so all I have to do is import the last backup of my virtual web hosts and I am good to go :)

I guess any OS would be fine, I was just wondering if there was a certain OS that may have focused more on the development of good software raid. As for what TYPE of RAID to use well RAID 0 is no good because its "STRIPING" and that means if loose one drive I loose all of the data . If I go with RAID 1, "MIRRORING" I would be writing the same data to 2 disks and in the event of one crashing I could replace or re-build the array with out bringing the system down for any longer than needed. RAID 5 well I didn't want to try that yet but I think I might.... PARITY BIT, if one drive fails I can replace it.... HOT SWAP well I don't have the space in my home server.

Hope this helps you to understand my situation a little better.

mostlyharmless 07-02-2008 04:21 PM

What type of RAID? I think 1+0 or 0+1 are both popular and simpler than RAID 5 in that they are supported by cheaper hardware (firmware raid) for booting; helpful if you want to put the whole system on RAID as opposed to just /home or other directories. Both 0+1 and 1+0 provide some speed advantage and redundancy are can survive more than one disk failure, depending on the setup. Having a "spare disk" is helpful too.

Whether or not you use mdadm to setup your RAID (nice because it uses a persistent superblock) or use a firmware board is probably not important once the RAID is setup - they're both software RAID.

Distros: I think Slackware is very straightforward and transparent and makes maintenance of RAID relatively painless, but I'm biased and no doubt everyone has a favorite distro. I don't know of any numbers to support superiority of speed for any distro or evidence that any one is more focused on RAID; perhaps an "Enterprise" commercial version such as Redhat might be, since it is my impression that they are more often installed on commercial servers with *real* RAID hardware. I don't know CentOS; it's probably fine.

For recover from failure, it depends on the mode of failure. A single disk failure not bringing down the RAID means just replacing the disk - that's the whole point of redundancy. If the RAID goes down, then you have to find out what failed, (with a boot rescue disk) replace it, and use the bare metal backup.

kenoshi 07-02-2008 07:17 PM

In terms of storage options, at install SLES 10+ IMO has the best file system, RAID, and volume management out the box (you can even do EVMS during install)...it even deals with multipathing at install (their udev rules with DID/persistence need some work, but so do most distros lol). They are also more up to date/responsive with file system/storage patches in general.

Redhat/CentOS wants you to do everything in LVMs...and IMO are slow to fix issues on the storage side. But yep, I don't think there is a difference in distros and storage performance either...stability in the different kernel versions used for each distro storage-wise is probably a greater concern TBH.

With regards to raid levels...depends on what you do. RAID 10 or 01 are great if you have the drives, but obviously capacity becomes an issue. For mostly reads, RAID5 is great and gives you more space for the buck, its write performance is fair.

bskrakes 07-03-2008 10:57 AM

Hi, thanks for the posts mostlyharmless and kenoshi.... I re-formatted and went with CentOS 5.0 Software RAID 5. I couldn't go RAID 0+1 or RAID 1+0 because it's not supported at the software level OR IS IT? In any case the RAID 5 is working well so far. I have about 400GB of media files that have to get transferred over and I think that will take a while but I can live with that as long as they are backed up in two places (in my case 3). Next step is to get my VMware Server backup and running.

Thanks again for your time! If I have any other questions I will post back... cheers!

mostlyharmless 07-04-2008 09:52 AM

Glad it's working for you. FYI Raid 0+1, 1+0 or any nesting is supported by mdadm...

bskrakes 07-04-2008 01:09 PM

Right on, I figured that it should and would be supported but I didn't see an option when partitioning. The RAID 5 seems to be working better than I expected and performance is great. 250 some GB's just under 1.5 days to transfer, of course that doesn't count some of the rebooting and down time....

Thanks again for your posts and help!!


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