Guest Adelxt Posted March 4, 2008 Posted March 4, 2008 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 Posted March 4, 2008 Posted March 4, 2008 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 Posted March 4, 2008 Posted March 4, 2008 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 Posted March 5, 2008 Posted March 5, 2008 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] Posted March 5, 2008 Posted March 5, 2008 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 Posted March 5, 2008 Posted March 5, 2008 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 Posted March 5, 2008 Posted March 5, 2008 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 Posted March 5, 2008 Posted March 5, 2008 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 > >
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