04-29-2011
Often, the bootstrap is on a simple disk, and the RAID is dedicated to the application. For software RAID, I wonder if that is a requirement, since you need to boot the software to get it together. Remember that raid5 is not churn-friendly or small-block-random efficient, so many shops put high-churn and small block-random data on mirrors, sometimes striped for more bandwidth. Also, the controller(s) can be a bottleneck. Even with lots of RAM, random operations on large data sets will fill RAM uselessly, and fsync() of RDBMS Commit and other critical files (postfix email) waits for magnetic completion. A shot of SSD might be a great complement. Sometimes, you can shadow the SSD with RAID5 hierarchically, so only the most accessed bits move to SSD. Too much modified data in RAM in a liability!
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LEARN ABOUT XFREE86
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