Best RAID 5 approach?

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Best RAID 5 approach?

Postby overflow » Tue Oct 04, 2005 4:50 pm

I am about to buy a new file server. It will be solely a file server but needs to be good at it. The primary concerns are cost, reliability and performance - probably in that order.

It will run Linux and it will sit in a rack, have RAID and a 1Gb interface. More than that, I haven't really decided yet.

The big unknown at the moment is how to implement the RAID. I want about 600GB available probably over 5 disks with a hot-spare. The options as I see it are:

* SCSI Raid controller
* ATA Raid controller
* Regular SCSI - software RAID
* Regular ATA (Serial/Parallel?) - software RAID

That's for the data. I'm also expecting to mirror the system disk as a separate measure.

Does anyone have any real experience with this who can recommend an approach? I really like the idea of keeping the hardware side simple and doing the RAID in software. Can I mirror the system drive in software?

All advice gratefully received.
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RE: Best RAID 5 approach?

Postby linuxgirlie » Tue Oct 04, 2005 5:28 pm

The problem with software raid at the moment is that you will need a spare hard drive just for the OS. I use software raid for my file servers which have two 300gb hard drives for storage and a 80gb for the os.
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RE: Best RAID 5 approach?

Postby wyliecoyoteuk » Tue Oct 04, 2005 8:29 pm

Actually, you can run raid mirroring with 2 disks, md devices will function on partitions, so we have set up storage servers with :
disk1: small root partition and large data partition
disk2: (unmounted) copy of root partition on disk1 and data partition equal in size to the data partition on disk 1

the 2 secondary partitions are set up as a raid mirror.

The beauty of this is if the primary disk fails, you can boot from a floppy and restore using the secondary root partition.
This sort of configuration is easy to set up when installing Suse, and I assume, Redhat or Mandriva.

There are several howtos on the net, but if you want to run striping with a hot spare, you are best using a dedicated controller card.
We have used an Adaptec PATA Raid card for that setup (4+1) on our redhat 7.3 server, and it performs pretty well, and the linux support is OK, although SATA might be the way to go.

Other than software raid, be aware that some Motherboards have SATA or IDE raid controllers which are really software based, and will often only work with windows.
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RE: Best RAID 5 approach?

Postby CJLL » Tue Oct 04, 2005 9:12 pm

I've been look at this myself, my thoughts were to build a system around http://www.adaptec.com/worldwide/produc ... t=Products

Scan do a good range of hot swap drive bays, anybody know of somewhere better?

However you might find life easier just buying a prebuilt unit

http://www.adaptec.co.uk/worldwide/prod ... orage+(NAS)+-+Snap+Servers&language=English%20UK

Bear in mind the doing RAID in software means you'll forfit hot swap capability.
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RE: Best RAID 5 approach?

Postby drws » Tue Oct 04, 2005 10:31 pm

I've got a few servers running RAID5 on the 3Ware sata cards. (9xxx series)
Driver support has been in the kernel since about 2.6.5ish, but 3Ware have always had drivers.
They come in upto 4,8 and 12 disk versions and they've started on Sata2 cards. (not tried these yet)
As the raid is done in hardware, it makes it a lot easier to use, and you can have / on it as well.

All the other servers we use have the HP/Compaqs 5i/6i SCSI Raid controller which is also very nice to use, but means spending a lot of cash.

If you go down the software route, setup a test system and then kill a disk. Get used to the commands for replacing failed disks etc.
The last time I tried it (about 3 years ago) a slight typo lost me all the data.
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Re: RE: Best RAID 5 approach?

Postby nelz » Tue Oct 04, 2005 11:15 pm

wyliecoyoteuk wrote:The beauty of this is if the primary disk fails, you can boot from a floppy and restore using the secondary root partition.


You don't need a boot floppy to do this. Add two entries to your bootloader menu, one to boot form the first disk and one from the second. If the first root partition fails, you can still boot from the backup. Also, install the bootloader to the second disk. Then, if the first disk fails completely, you can still boot from the second disk.
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RE: Re: RE: Best RAID 5 approach?

Postby wyliecoyoteuk » Wed Oct 05, 2005 8:18 pm

nice one nelz, I hadn`t thought of sdoing it that way,. it was just the best mirror solution we could come up with at short notice.
we also set up a udev rsync script to back up to an USB hard disk, for offsite backup the customer loves it, and following a severe weekend power spike, we could recover his file server in less than 30 minutes.
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