Raid 5

HelterSkelter

Lads,

was thinking of setting up RAID 5 on my home PC. Does anyone have any experience of it?

I currently have a 120GB disk which I backup onto a second 120GB disk using Norton Ghost. According to http://www.pcguide.com/ref/hdd/perf/raid/levels/singleLevel5-c.html with 3 120GB disks I will have a storage capacity of 240GB.

Only thing I am concerned about is the speed of the write. I am using IDE disks.

Please reply with tips/comments.

Thanks.

colm_c

There's 2 types of RAID really software and hardware.

With software you let windows/mac os/linux do all the work as well as keeping the system going. (This is usally built-in to the OS)

But with Hardware, you have a controller card - usually a PCI card connected to all of the drives with it's own memory and processing power. (These can cost anywhere from 50euro to 5k)

The software RAID can be a tad slow depending what you plan to do with it, but the hardware RAID is pretty fast.

Don't forget that if you have 3 drives configured in RAID 5, you'll need a hot spare so if one becomes faulty then you can just swop it out. If you don't have a hot spare then you'll have to wait until you get one to get your machine online again.

RAID is generally used on fileservers and backup machines rather than on desktops. You'd almost be better getting an external hard-drive and use that for backing up.

HelterSkelter

colm_c wrote:

There's 2 types of RAID really software and hardware.

I'll get a RAID controller card. They seem to be around €130 for RAID 5.

colm_c wrote:

RAID is generally used on fileservers and backup machines rather than on desktops. You'd almost be better getting an external hard-drive and use that for backing up.

That's the cheaper alternative alright but I hate the fuss of setting a backup going and leaving the PC on all night (it's in my bedroom and the noise pisses me off!!). With RAID it would be all automated.

Another question, my existing XP installation and data (mp3's, mpegs, etc) are on the 120GB drive which is one of the drives I plan to use for RAID. When setting up RAID do I need to have all 3 drives formatted? If so this means I will need a fourth 120GB to store the data while setting up RAID. Am I right?

colm_c

When you're getting the controller, just make sure you get one that supports IDE, I'm not sure if any of them do, all the ones I've set up were using SATA drives... but maybe I'm wrong.

You'll have to take everything off it alright, with the controller, the PC just recognises the RAID system as one large volume and will need to format it as one, all the RAID config is done when you boot, before you load on the OS.

As for any backup solution, it shouldn't take that long (ok maybe the first time) if you're syncing it, with incremental updates.

RAID alone isn't a backup, it merely gives fault tolerance, which means if one drive goes down/gives up/starts spewing smoke - you stick in the spare (or switch it over to the spare) and the data can be rebuilt via the 2 other drives to form the complete data set again.

HelterSkelter

colm_c wrote:

As for any backup solution, it shouldn't take that long (ok maybe the first time) if you're syncing it, with incremental updates.

Hmm, maybe you are right and I should be backing up instead. Up to now I was using Norton Ghost to backup to a second 120GB internal HD. It was taking about 8 hours. Is there a better backup solution I could use instead?

Thanks for the help.

Inspector Gadget

Something that may be relevant is that going the hardware RAID route may tie you down to the type of controller card you go with - if the card itself fails, and you can't get a replacement (or a compatible one, which will probably mean a later model from the same manufacturer), you're well scuppered. Software RAID, although it's a bit slower, ends up being more fault-tolerant as you can chuck out your controller/motherboard/whatever, replace it with something completely different, and carry on - this you can't do with a hardware controller.

[edit]Another thing - price up cards capable of RAID5 (as opposed to 0/1/0+1, as the cheap ones offer)... make sure you're sitting down first though [/edit]

At least, this is what I'm told
Gadget

Mac daddy

Inspector Gadget wrote:

Something that may be relevant is that going the hardware RAID route may tie you down to the type of controller card you go with - if the card itself fails, and you can't get a replacement (or a compatible one, which will probably mean a later model from the same manufacturer), you're well scuppered. Software RAID, although it's a bit slower, ends up being more fault-tolerant
Gadget

Erm no have you any exprience using raid to start of with -

From My personal exprience (Dealing with this everyday and Vraid's)
Software raid is not better than hardware - only good point about it is its cheap and that is it nothing else,

Software raid a single bit out line will stop a rebuild from happening we have seen this several times, it is a nightmare to use and to have.

Hardware raid - for instance why do you even want raid 5 - means min of 3 drives and it is not faster than raid 0 for instance-
It is good for databases if you have a read/write modules attached the controller, otherwise this is going to slow down the performance big time.2x writes and finaly parity write + you will notice you will lose space on the raid set due the equivilent of one disk you will be lost this is your parity spread over three drives - so that will be 120+120+120 -parity = 240Gig

And if your data is on one of the 120Gig hdd's that is not in a raid yes - for a hardware raid you will need to format - configure raid -Install the driver for the controller and install the OS.

You might better off with a raid 0+1 solution

colm_c

Hmm, maybe you are right and I should be backing up instead. Up to now I was using Norton Ghost to backup to a second 120GB internal HD. It was taking about 8 hours. Is there a better backup solution I could use instead?

With norton you should be able to do an incremental backup, it's one of the options afaik.

The built in windows backup software does it too... and there's loads of backup software, shareware on the net that can do the job.

8 hours sounds like far too long, unless you're copying over every single file again...

HelterSkelter

Mac daddy wrote:

for instance why do you even want raid 5 - means min of 3 drives and it is not faster than raid 0 for instance-

I don't know what I want to be honest!!

The 3 disks for RAID are not a problem, I already have 2 x 120GB so I will need to buy another (and borrow one too!).

I have about 80GB of Multimedia which I want to back up. Also want to back up my Documents/XP Settings/Emails/etc etc. If one of my drives does go bust I want to be able to restore easily with minumum fuss.

Inspector Gadget

@Mac daddy: Fair enough - am only relaying what other people have warned me about, am not claiming to be a guru or any such thing in the area. I've got a mixture of hardware and software RAID setups scattered about here (RAID-1 with IDE disks - don't laugh too much, okay? - though I suppose they are spread out across Windows, Linux and MacOS boxes) so I know a little bit, but certainly not from an enterprise perspective - but then again I don't think that's what we're talking about here. (I don't know how good Windows is with software RAID either, for reference)

The truth of the matter, though, is that most of us mere mortals are only getting warmed up to the idea of what RAID is and what it does - and from my limited experience (comparatively speaking, anyway, though we're agreeing here) RAID 5 sure seems like overkill, especially given the cost of the controllers compared to the cheaper (if crappier) controllers out there that most of us are using. RAID-0+1 seems to be a good compromise of speed and reliability (at least from a theoretical perspective), though it'd require four drives?

Anyway, I'll shut up now...
Gadget

alantc

A question for you all,

With RAID5, can you gradually add disks as you need more space or do all the disks need to be in the array when you make it. Maybe it's possible like hot swapping?

And when DVD drives become SATA, will it be any problem having it on the same controller as a few disks that are in an array?

W.

HelterSkelter

I'm thinking of going for an external hard drive now as colm_c suggested. Was thinking of the Maxtor Onetouch II, what do you think of this price?

http://www.komplett.ie/k/ki.asp?sku=303455&cks=PLS

mp3guy

looks good, but how fast is your internal hard drive?

HelterSkelter

mp3guy wrote:

looks good, but how fast is your internal hard drive?

One is 7200 RPM, not sure about the other.

leeroybrown

HelterSkelter wrote:

I currently have a 120GB disk which I backup onto a second 120GB disk using Norton Ghost.

You seem to be bringing 'RAID' and 'backup' into the same thread. RAID offers redundancy (ie. The ability to recover from a drive failure) but it is not a backup system. A backup should survive a failure of the original source but a RAID array could have a multiple drive failure, have a controller failure or replicate faulty data to all mirrors/checksums. It also adds an additional layer of complexity/failure. RAID is excellent when you want redundancy and uptime but you still need backup. Ultimately if you are looking at a backup solution then RAID is not it.

As an example, I had a power surge take out both disks of a RAID1 setup last year. The backup came in handy. Conversely, a friend had a kernel level file system error that replicated itself to both disks of a RAID1 mirror. The lack of a backup cost him a lot of data. These are freak occurrances - but freak occurances are why you backup.

glasgowspremier

alantc wrote:

A question for you all,

With RAID5, can you gradually add disks as you need more space or do all the disks need to be in the array when you make it. Maybe it's possible like hot swapping?

And when DVD drives become SATA, will it be any problem having it on the same controller as a few disks that are in an array?

W.

No answer yet for alantc> I have a similar sort of query. Any insight would be appreciated.
I have a file server with an array of 3 x 72Gb disks configured for RAID5, i.e. offering 123Gb of storage. I need to increase the storage available. Does anybody have an advisable course of action? Should I
A) Buy one disk and add it to this single array? If so, how much extra storage would I get by installing an additional 72Gb disk?
Purchase 3 x 72Gb disks and create a new array?

It is so long since I initially set up this server that I have kind of forgotten what I did. It is not really the sort of thing I do every day.

Thanks in advance for any help.

SwampThing

glasgowspremier wrote:

No answer yet for alantc> I have a similar sort of query. Any insight would be appreciated.
I have a file server with an array of 3 x 72Gb disks configured for RAID5, i.e. offering 123Gb of storage. I need to increase the storage available. Does anybody have an advisable course of action? Should I
A) Buy one disk and add it to this single array? If so, how much extra storage would I get by installing an additional 72Gb disk?
Purchase 3 x 72Gb disks and create a new array?

It is so long since I initially set up this server that I have kind of forgotten what I did. It is not really the sort of thing I do every day.

Thanks in advance for any help.

Short answer; depends. Some array controllers and their associated management applications allow you to expand a logical volume, but it's up to the OS if it can 'see' and 'use' the extra space provided. XP & W2K, afaik, can grow a volume if the volume is setup as a dynamic disk - someone will correct me here no doubt.
If you add a drive to a RAID 5 array, it'd have to rebuild the entire volume as it spreads data across the new disk. Can be time-consuming, especially with software RAID.
The €50-controllers mentioned here are not likely to give you this sort of flexibility though.