RAID-1 Vs RAID-5

[Kingy]

Hi all,

Just wanted to clarify a couple of things regarding RAID if possible.

I know that you need 3 Drives for RAID-5, and that if one disk fails, then the server remains live. What happens when a disk dies? I was under the impression that you just unplugged the dead disk, and plugged in a new one and voila. Is this correct?

What happens when a disk dies in RAID-1? Does the server remain live? How is the array restored in the event of a failure?

Can a RAID 1 array be 'upgraded' to RAID 5 by adding an extra identical disk? Does identical disk mean one that's the same size, or just the same manufacturer, or even the same model number?

If you run out of space on a RAID-1 array, can a RAID-5 array be added to the same RAID controller?


Any help appreciated, many thanks.

 

[rpstewart]

I know that you need 3 Drives for RAID-5, and that if one disk fails, then the server remains live. What happens when a disk dies? I was under the impression that you just unplugged the dead disk, and plugged in a new one and voila. Is this correct?

Pretty much correct, it's not quite voila but near enough - might take a few hours to rebuild the array onto the replacement but virtually every controller will let you do it in the background while you keep working.

What happens when a disk dies in RAID-1? Does the server remain live? How is the array restored in the event of a failure?

Server will remain live, again you should be able to rebuild onto the replacement while still working. Probably will be a quicker rebuild as there's no parity information to calculate.

Can a RAID 1 array be 'upgraded' to RAID 5 by adding an extra identical disk? Does identical disk mean one that's the same size, or just the same manufacturer, or even the same model number?

Depends on the controller here. I know my RocketRAID card can do this and I'd assume most decent cards would as well. Identical drives may not be required - I'm using a mix of Hitachi 7K250s and T7K250s at the moment without any issues. I've had arrays with mixed size disks in machines at work in the past too.

If you run out of space on a RAID-1 array, can a RAID-5 array be added to the same RAID controller?

Assuming you've got at least 5 ports on the controller then that should be possible.

 

[Elric]

A Raid 1 system will continue to work when a single disk fails.

Most Raid controllers will auto repair once a defunct disk has been replaced. Cheaper ones may not auto start the process.

Some controllers DO allow you to change the raid configuration from any of the supported raid leves.

Depending upon the controller it can also support multiple raid volumes of different raid types.

I know a lot of what is said above is vague, but it is really down to what the specific controller supprts in terms of RAID and features.

Hope this helps.

 

[Kingy]

Server will remain live, again you should be able to rebuild onto the replacement while still working. Probably will be a quicker rebuild as there's no parity information to calculate.

Is this the case when using Software RAID-1? I can't imagine that the <£200 saving on only buying 2 disks instead of 3, while halving the available capacity is enough of a reason not to choose RAID-5, so I'm imagining that the main saving is the lack of a need for a hardware RAID controller?

Depends on the controller here. I know my RocketRAID card can do this and I'd assume most decent cards would as well. Identical drives may not be required - I'm using a mix of Hitachi 7K250s and T7K250s at the moment without any issues. I've had arrays with mixed size disks in machines at work in the past too.

Assuming that RAID-1 is implmented on a hardware RAID controller that can do this, is it possible to do this 'on-the-fly', ie without downtime, or more importantly, without having to re-format?

I know a lot of what is said above is vague, but it is really down to what the specific controller supprts in terms of RAID and features.

How would I find out what a RAID card supports? What terms am I looking for etc?

Are PERC4/Di - PERC4/DC - PERC4/SC controllers any good and what are the differences?

Also, is it possible to add an extra disk to a x disk RAID-5 array to increase capacity either 'on-the-fly', or without formatting?


Thanks to both for your help.

 

[Elric]

Are you asking specifically about Server RAID? Server RAID controllers offer far superior functions than the PC motherboard counterparts.

A controller such as the PERC series controller, allow for failure to be restored on the fly with minimal user effort. One of the main aspects of a server RAID card is Resilence and fault tolerance whilst also providing enhanced performance.

BY Design, they are configured to give you a flexible approach to rebuild / expansion or reconfiguration.

 

[Kingy]

Are you asking specifically about Server RAID? Server RAID controllers offer far superior functions than the PC motherboard counterparts.

A controller such as the PERC series controller, allow for failure to be restored on the fly with minimal user effort. One of the main aspects of a server RAID card is Resilence and fault tolerance whilst also providing enhanced performance.

BY Design, they are configured to give you a flexible approach to rebuild / expansion or reconfiguration.

Yes, specifically server RAID, albeit at the budget end of things...

Where might I be able to find out more about PERC cards etc?

Will software RAID-1 done in windows remain 'live' in the event of a disk failure? Can the array be recreated in the event of a disk failure (or indeed actually created) 'on the fly'?

 

[Mercutio]

Yes, specifically server RAID, albeit at the budget end of things...

Where might I be able to find out more about PERC cards etc?

Will software RAID-1 done in windows remain 'live' in the event of a disk failure? Can the array be recreated in the event of a disk failure (or indeed actually created) 'on the fly'?

Windows software raid 1 will remain live in the event of a failure. Generally the "best" way to actually make a raid 1 is to have it as a single disk you add a partner to. Something else to note - this ones from experience is to NOT have the OS on the raid. If it ever goes **** up you have many more ways to recover once you boot from single drive and get into a nice easy GUI with a net connection

 

[Kingy]

Windows software raid 1 will remain live in the event of a failure. Generally the "best" way to actually make a raid 1 is to have it as a single disk you add a partner to. Something else to note - this ones from experience is to NOT have the OS on the raid. If it ever goes **** up you have many more ways to recover once you boot from single drive and get into a nice easy GUI with a net connection

But surely then you have no redundancy on your boot partition/disk?