RAID 5 System

[Valiant]

God I feel so out of it, I haven't had my hands building a PC or server for quite a while so I was thinking of solving the small office IT problems with a homebuilt NAS unit. Am I right in thinking that all I'll need are PC Case, Motherboard, RAID card, HDs and Software?

[Greenbank]

Software or hardware RAID? The latter is, obviously, better as it uses less CPU.

Raid 5 requires a minimum of 3 HDDs. Make sure the case/PSU (and motherboard for software RAID) can support this.

IMHO, all in one box is neater than external drives floating about.

I'm looking for a NAS box too although I'm going to buy a dedicated NAS device rather than yet another machine.

[Valiant]

Hardware, I was thinking lowish power CPU and 2GB ram, I want the ability to have upto 10 disks. So I guess I'm looking at a full size tower with individual 5.25 hot swap caddies.

[andygates]

Yup.  At least three, more is better. 

[Valiant]

I'm liking that with 5 external and 6 internal. Very pretty too.


I'm also liking that for the huge 11x external bays.

[TimO]

Also remember, if you do go the hardware RAID way, you need to have a spare controller card.  There is little point having a bomb proof set of discs, if the controller goes Boom, and you can't get a replacement.  You then have a set of discs with all you data on, and no way to get to it (different hardware controllers can store the RAID differently on the discs).

This is at least one advantage of a software RAID, you can plug the discs into another machine altogether, so long as it has the same physical connections (eg likely to be SATA/SAS these days) and then just install suitable software.

[Valiant]

Isn't software slower? As it's agoing to be a dedicated storage server, I'm not fused about CPU use as it'll have a 2Ghz dual core sitting there doing nowt.

[Valiant]

Ok well I guess software raid looks to be the easier in the long run, anyone know any motherboards with a lotta sata connectors?

[TimO]

I've actually got a RAID controller configured as JBOD, just so that I can use software RAID.  After some testing of hardware vs software RAID, I decided that the controller was actually pretty damned useless at doing the hardware RAID anyway, so there was only a very slight impact performance wise switching to software.  This also has the advantage that I can share the same hot spare disc between three different RAID arrays, which wasn't an option with the hardware RAID.

[Valiant]

Can anyone get any trade deals on hard drives via work? I'm after 8x1TB SATAII HDs

[rae]

I decided that the controller was actually pretty damned useless at doing the hardware RAID anyway, 

I have been burned far too many times by software RAID flaking out under load.   It's all fine until you really hit it, then a bunch of updates don't get calculated and you're in rebuild territory. 

RAID is for performance and availability - it is not for backup.  Logical and physical failure will send you to back up, not a new controller (IMO) though a spare controller is good insurance if your backup sucks.  If the controller dies, it will frequently take the disks with it, and anyway, the most probable failure is in software rather than in hardware.   In the average 3 disk RAID set, the probability of disk failure is generally lower than "other hardware" failure.   If you're playing with 20 disk sets, then it swings round, but you'd be running RAID 6 by then.

These days I'd rather build a 64 bit system with 16 GB of buffer than piss about with RAID at the SOHO level unless I really need the capacity in a single file system.   SATA RAID performance sucks anyway when you break through the buffer and hit the disk.   Burst figures are great, sustained is something else.   YMMV - depends what you want to do with it.

If you want to do SATA RAID in SOHO land, then get an Areca or similar controller and institute good backups.  Shove a shed load of memory in the host, and get a decent network card.  If you're above SOHO, get a proper solution, assuming money depends on it.

[Valiant]

It's really a fileshare of databases, spreadsheets, word docs, photos and quicktime video (1GB file). It works out about the same cost and bigger space than replacing all the 6 SCSIs to higher capacity discs. It's all backed up every night to tape. I reckon for that ise SATA is fine as there isn't much sustained use on the discs. The main system will still live on the SCSIs on the main server.

[vorsprung]

Also remember, if you do go the hardware RAID way, you need to have a spare controller card.  There is little point..

disks have moving parts and are far more likely to fail

This is at least one advantage of a software RAID, you can plug the discs into another machine altogether, so long as it has the same physical connections (eg likely to be SATA/SAS these days) and then just install suitable software.
[/quote

Mind you that is true]

[TimO]

Discs are more likely to fail, and for that matter, so are many other parts of the hardware, but the controller card could fail, and Sods Law dictates that it is likely to at the most inopportune moment.

If the controller does fail, and you start looking around for a replacement, and find out it's out of stock for a month, or worse, no longer manufactured, you are stuffed big time.

Discs of the same size (or bigger) can always be acquired, so can most mass market commodity PC bits, or at least something which will be close enough to the original system to run what you need to run.  Without a suitable matching controller, you can't get to the data, although to be fair, as others have said, you should have backups, but they could still be missing some vital recent change to the data.