Raid 5 with 4 drives

[Guest Adelxt]

Hi,

 

I'm presently running a raid 5 with 3 drives. If two of the three drives

fail, then I would have to re-install the OS and restore from backup. If I

use 4 drives for a Raid 5, would I not have to restore the OS until three of

the 4 drives failed? Would it be 4 of 5 drives if I chose to have a Raid 5

using 5 drives.

 

What I'm thinking is that the possibilities of more then two drives failing

at once is slim but if that happens I could still keep my OS intact if I

used a Raid 5 of 4 drives or more.

 

Thanks

Steve

[Guest Meinolf Weber]

Re: Raid 5 with 4 drives

 

Hello Adelxt,

 

Doesn't matter how many drives your RAID5 has, one drive fails, it will rebuilt

the information, 2 drives fail, your lost. Even RAID5 does NOT prevent you

to have good and tested backups.

 

Best regards

 

Meinolf Weber

Disclaimer: This posting is provided "AS IS" with no warranties, and confers

no rights.

** Please do NOT email, only reply to Newsgroups

** HELP us help YOU!!! http://www.blakjak.demon.co.uk/mul_crss.htm

> Hi,

>

> I'm presently running a raid 5 with 3 drives. If two of the three

> drives fail, then I would have to re-install the OS and restore from

> backup. If I use 4 drives for a Raid 5, would I not have to restore

> the OS until three of the 4 drives failed? Would it be 4 of 5 drives

> if I chose to have a Raid 5 using 5 drives.

>

> What I'm thinking is that the possibilities of more then two drives

> failing at once is slim but if that happens I could still keep my OS

> intact if I used a Raid 5 of 4 drives or more.

>

> Thanks

> Steve

[Guest dan]

Re: Raid 5 with 4 drives

 

Adelxt, the short answer is that Raid 5 protects you against 1 drive

failure. If you have more than one drive fail at the same time you are

looking at a reinstall. Raid 5 stripes both data and parity information

across 3 or more drives. The fault protection works by ensuring that the

parity information for any given block of data is written on a separate

physical drive from the data. That means any block of data can be faithfully

restored if one drive fails. If two drives fail, the data cannot be restored

from the parity information.

 

"Adelxt" <sales@adelxt.com> wrote in message

news:OA8JiGkfIHA.4728@TK2MSFTNGP03.phx.gbl...

> Hi,

>

> I'm presently running a raid 5 with 3 drives. If two of the three drives

> fail, then I would have to re-install the OS and restore from backup. If I

> use 4 drives for a Raid 5, would I not have to restore the OS until three

> of the 4 drives failed? Would it be 4 of 5 drives if I chose to have a

> Raid 5 using 5 drives.

>

> What I'm thinking is that the possibilities of more then two drives

> failing at once is slim but if that happens I could still keep my OS

> intact if I used a Raid 5 of 4 drives or more.

>

> Thanks

> Steve

>

>

[Guest PaulMaudib]

Re: Raid 5 with 4 drives

 

On Tue, 4 Mar 2008 16:50:51 -0500, "Adelxt" <sales@adelxt.com> wrote:

>Hi,

>

>I'm presently running a raid 5 with 3 drives. If two of the three drives

>fail, then I would have to re-install the OS and restore from backup. If I

>use 4 drives for a Raid 5, would I not have to restore the OS until three of

>the 4 drives failed? Would it be 4 of 5 drives if I chose to have a Raid 5

>using 5 drives.

>

>What I'm thinking is that the possibilities of more then two drives failing

>at once is slim but if that happens I could still keep my OS intact if I

>used a Raid 5 of 4 drives or more.

>

>Thanks

>Steve

>

 

If you are using RAID 5 on three drives and lose 1, you've lost the

entire thing. RAID 5 requires MINIMUM 3 drives to operate. Lose on

and you've lost your fault tolerance. For fault tolerance, you need

to add at least one more drive.

[Guest Lanwench [MVP - Exchange]]

Re: Raid 5 with 4 drives

 

Adelxt <sales@adelxt.com> wrote:

> Hi,

>

> I'm presently running a raid 5 with 3 drives. If two of the three

> drives fail, then I would have to re-install the OS and restore from

> backup. If I use 4 drives for a Raid 5, would I not have to restore

> the OS until three of the 4 drives failed? Would it be 4 of 5 drives

> if I chose to have a Raid 5 using 5 drives.

>

> What I'm thinking is that the possibilities of more then two drives

> failing at once is slim but if that happens I could still keep my OS

> intact if I used a Raid 5 of 4 drives or more.

>

> Thanks

> Steve

 

In addition to the other replies - if you've got a spare bay & your card

supports it, get another identical drive & configure it as a hotspare. This

will help you if *two* drives fail - and yes, that can happen. It will also

keep your disks from running in degraded mode if you have a single drive

fail.

[Guest Peter Lawton]

Re: Raid 5 with 4 drives

 

Also if your RAID controller supports ADG RAID then you can set it up to

have more than one parity drive and thus protect you from more than one

drive failure.

 

I usually go for RAID 10 myself both for the added resiliency and the much

better performance.

 

Peter Lawton

 

"Adelxt" <sales@adelxt.com> wrote in message

news:OA8JiGkfIHA.4728@TK2MSFTNGP03.phx.gbl...

> Hi,

>

> I'm presently running a raid 5 with 3 drives. If two of the three drives

> fail, then I would have to re-install the OS and restore from backup. If I

> use 4 drives for a Raid 5, would I not have to restore the OS until three

> of the 4 drives failed? Would it be 4 of 5 drives if I chose to have a

> Raid 5 using 5 drives.

>

> What I'm thinking is that the possibilities of more then two drives

> failing at once is slim but if that happens I could still keep my OS

> intact if I used a Raid 5 of 4 drives or more.

>

> Thanks

> Steve

>

>

[Guest Daniel Crichton]

Re: Raid 5 with 4 drives

 

PaulMaudib wrote on Tue, 04 Mar 2008 18:11:57 -0600:

> On Tue, 4 Mar 2008 16:50:51 -0500, "Adelxt" <sales@adelxt.com> wrote:

>> Hi,

>> I'm presently running a raid 5 with 3 drives. If two of the three

>> drives fail, then I would have to re-install the OS and restore from

>> backup. If I use 4 drives for a Raid 5, would I not have to restore

>> the OS until three of the 4 drives failed? Would it be 4 of 5 drives

>> if I chose to have a Raid 5 using 5 drives.

>> What I'm thinking is that the possibilities of more then two drives

>> failing at once is slim but if that happens I could still keep my OS

>> intact if I used a Raid 5 of 4 drives or more.

>> Thanks

>> Steve

 

> If you are using RAID 5 on three drives and lose 1, you've lost the

> entire thing. RAID 5 requires MINIMUM 3 drives to operate. Lose on

> and you've lost your fault tolerance. For fault tolerance, you need to

> add at least one more drive.

 

If you lose 1 drive in RAID 5 you do not lose the entire array - the other

drives hold the parity information to rebuild the failed drive. I've had

drive failures in RAID 5 systems with 3 drives and recovered them by

swapping the failed drive for a new one and rebuilding, just like in RAID 5

setups with more drives.

 

I'd avoid using systems with RAID 5 with 3 drives though - apart from the

couple I have here for development use, the other serves all have RAID 5

with 5 drives + 1 hotspare, or RAID 10 across 2 arrays of 3 or more drives

per array.

 

--

Dan

[Guest John Whites]

Re: Raid 5 with 4 drives

 

I think what you're wanting to do is RAID 6.

 

-John

 

"Adelxt" <sales@adelxt.com> wrote in message

news:OA8JiGkfIHA.4728@TK2MSFTNGP03.phx.gbl...

> Hi,

>

> I'm presently running a raid 5 with 3 drives. If two of the three drives

> fail, then I would have to re-install the OS and restore from backup. If I

> use 4 drives for a Raid 5, would I not have to restore the OS until three

> of the 4 drives failed? Would it be 4 of 5 drives if I chose to have a

> Raid 5 using 5 drives.

>

> What I'm thinking is that the possibilities of more then two drives

> failing at once is slim but if that happens I could still keep my OS

> intact if I used a Raid 5 of 4 drives or more.

>

> Thanks

> Steve

>

>