failing drive Post: 302216787

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Operating Systems AIX failing drive Post 302216787 by bakunin on Monday 21st of July 2008 06:58:05 AM

07-21-2008

Registered User

How this is exactly done is depending on the RAID adapter (more precisely: the adapters driver software), so i can give you only general directions.

If the failing disk is part of a RAID you will probably not be able to manage the disk device itself. A RAID works like this: there are several disks connected to an adapter. The driver software of the adapter makes one big virtual disk out of the several physical ones and presents this virtual construct as a physical disk to the machine. (This is what is done during the "RAID initialization" or however it is called with your software. The driver/adapter writes some bookkeeping information onto the physical disk to be able to use them the described way.)

Only this virtual disk is added to a VG as a "Physical Volume" and from there on normal LVM procedures apply.

Your first task is to make the PV free from OS access. You can do this by either breaking the mirror (if the VG is mirrored) or by varying off the VG as zaxxon suggested. Since the "disk" in the VG is only a virtual construct there is no strict relationship between disks and logical volumes. All the logical volumes on the virtual RAID disk are "smudged across" the physical disks comprising the RAID.

After this you need to use the adapters driver software (in case of the IBM SCSI RAID adapter this is plugged into SMITty and the diag utility) to remove the disk from the RAID, after which the RAID is in status "reduced". then physically change the disks and add the new disk to the RAID. This will probably take some time as the new disk has to be written with the data first to be useful in the RAID. Only then varyon again and start using the VG again.

Do you need to backup? In principle you don't, because in a RAID all the disks hold all the information with redundancy. The classical case is 5 disks holding the capacity of 4 - for this penalty it is possible to replace every single disk without losing data, because the data it holds is also available on the other 4. This does NOT mean that a backup would be a bad idea: not at all! It is better to have a backup you don't need than to need a backup you don't have.

I hope this helps.

bakunin

bakunin

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ataraid

ATARAID(4)						   BSD Kernel Interfaces Manual 						ATARAID(4)

NAME

     ataraid -- ATA software RAID support

SYNOPSIS

     device ata
     device ataraid

DESCRIPTION

     The ataraid driver provides support for so-called software RAID (sometimes referred to as fake RAID or pseudo RAID).

     When a controller that supports software RAID is instructed to create a RAID array, its BIOS writes data structures in a specific metadata
     format to the disks.  These data structures are picked up by the ataraid driver, so that FreeBSD can work with the array.	The ataraid driver
     has to understand the specific metadata format of a controller BIOS in order to support its RAID capabilities.

     Read-only support for a metadata format means that FreeBSD can use the given RAID array for normal read/write operations.	Creation and
     rebuild of such arrays has to be done from the controller BIOS.

     Read and write support for a metadata format means that FreeBSD can use the given RAID array for normal read/write operations.  Additionally,
     the atacontrol(8) utility can be used to create, rebuild, update and fail such RAID arrays.

     The ataraid driver can read the following metadata formats:

     o	 Adaptec HostRAID
     o	 Highpoint V2 RocketRAID
     o	 Highpoint V3 RocketRAID
     o	 Intel MatrixRAID
     o	 Integrated Technology Express (ITE)
     o	 JMicron
     o	 LSI Logic V2 MegaRAID
     o	 LSI Logic V3 MegaRAID
     o	 NVIDIA MediaShield
     o	 Promise FastTrak
     o	 Silicon Image Medley
     o	 Silicon Integrated Systems (SiS)
     o	 VIA Tech V-RAID
     o	 FreeBSD PseudoRAID

     The ataraid driver can write the following metadata formats:

     o	 Highpoint V2 RocketRAID
     o	 Intel MatrixRAID
     o	 JMicron
     o	 Promise FastTrak
     o	 Silicon Integrated Systems (SiS)
     o	 VIA Tech V-RAID
     o	 FreeBSD PseudoRAID

     It is also possible to use software RAID on controllers that do not have special software RAID capabilities.  See atacontrol(8) for details.

FILES

     /dev/ar*  ATA RAID device nodes

SEE ALSO

     ata(4), atacontrol(8)

CAVEATS

     RAID5 is not supported at this time.  Code exists, but it neither uses nor maintains parity information.

AUTHORS

     The ataraid driver was written by Soren Schmidt <sos@FreeBSD.org>.  This manual page was written by Christian Brueffer
     <brueffer@FreeBSD.org>.

BSD
								 February 17, 2006							       BSD