RAID on Linux Post: 302816677

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Operating Systems Linux RAID on Linux Post 302816677 by verdepollo on Tuesday 4th of June 2013 11:50:29 AM

06-04-2013

Registered User

The main purpose of RAID is to provide some level of redundancy and/or performance gain (RAID 0) by using more than 1 disk.

If all your partitions reside on the same disk then there is no benefit of using RAID since in case of disk failure all your data will be gone regardless of RAID level. (E.g. RAID 5 won't be more "safe" than RAID 0).

In the case of RAID 0 where you're supposed to merge two or more disks together to achieve faster I/O operations, it's completely useless as your disk has a limited amount of mechanical heads and they cannot move faster than their assembly allows, so you'll see no I/O benefit either.

Software RAID also requires system resources (CPU, RAM, etc) as opposed to a *true* hardware RAID which provides its own electronic circuitry that handles the requirements.

Also, if your /boot partition is controlled by software RAID it's more difficult to recover in case of failure. Some systems won't recognise it as a valid partition and you'll need to perform some extra steps to work around the issue.

Software RAID is better than no RAID at all and may provide some benefits here and there, but a RAID array that uses partition that reside in the same disk is pointless.

verdepollo

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vxr5check

vxr5check(1M)															     vxr5check(1M)

NAME

       vxr5check - verify RAID-5 volume parity

SYNOPSIS

       /etc/vx/bin/vxr5check [-i | -v] [-g diskgroup] volume

DESCRIPTION

       The vxr5check utility compares the parity of each stripe of a RAID-5 volume specified by volume.  vxr5check reads the data for each stripe,
       generates the parity for this stripe, and compares this parity with the existing parity.

       vxr5check can be run against the entire RAID-5 volume, or incrementally on RAID-5 stripe boundaries, by specifying the -i option.

OPTIONS

       -g diskgroup
		 Specifies the Veritas Volume Manager (VxVM) disk group name for the RAID-5 volume name for verification.  If this option  is  not
		 specified, the default disk group is determined using the rules given in the vxdg(1M) manual page.

       -i	 Verifies the RAID-5 volume incrementally per stripes.	If a parity mismatch is found, that stripe location is displayed.

       -v	 Verbose output for the incremental vxr5check verification.  The verbose option outputs each stripe number that is being verified.

OUTPUT FORMAT

       In  verbose  mode and incremental mode, summary reports for each stripe of the RAID-5 volume are printed in output records.  If an error is
       returned for a stripe, then an error message and stripe number are displayed.  In non-verbose mode, if an error is returned, an error  mes-
       sage is displayed.

       If a parity mismatch error is determined on a stripe, vxr5check exits on that stripe and does not continue for the remaining stripes in the
       RAID-5 volume.

FILES

       /usr/lib/vxvm/bin/vxr5vrfy    The utility that vxr5check calls to perform RAID-5 parity verification operations for  the  specified  RAID-5
				     volume.

EXIT CODES

       The  vxr5check  utility exits with a non-zero status if the attempted operation fails.  A non-zero exit code is not a complete indicator of
       the problems encountered, but rather denotes the first condition that prevented further execution of the utility.

       See vxintro(1M) for a list of standard exit codes.

NOTES

       Do not run vxr5check on a volume that is in degraded mode.

SEE ALSO

       vxevac(1M), vxintro(1M), vxmend(1M), vxvol(1M)

VxVM 5.0.31.1							    24 Mar 2008 						     vxr5check(1M)