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Full Discussion: RAID5 + STRIPED LUNs
Special Forums Hardware RAID5 + STRIPED LUNs Post 302773079 by hicksd8 on Wednesday 27th of February 2013 09:38:58 AM
Old 02-27-2013
I assume by striped LUN's you mean software RAID.
Software RAID is "poor man's RAID".

I assume that you have a hardware RAID5 controller.

There is little point in using both at the same time. Software RAID uses CPU cycles which can be bad on a system loaded with apps.

Originally there was RAID3. This striped the data over a number of drives and also had a dedicated parity drive. This meant that every file write involved a write to the parity drive hence creating a bottleneck. So RAID5 was created.

RAID5 is striped data with rotating parity. The parity function is rotated between all the drives eliminating the bottleneck. I/O is spread across a number of actuators (drives) so the more drives in the RAID5 the greater the I/O bandwidth available. Compounding this functionality with software RAID is pointless. The hardware RAID5 controller will offload all I/O processing (parity calculation) from the main CPU of the box.

Dunno whether that answers you question(s) or not? Post back any further questions if not.

So RAID5 if good for general random I/O (mixed and unpredictable read/write)
In a situation where I/O's are predominantly read-only (eg, large Oracle database with mainly read enquiries) then RAID3 will be a bit faster because there's no need to read the parity if drives are healthy.
 

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MFI(4)							   BSD Kernel Interfaces Manual 						    MFI(4)

NAME
mfi -- LSI Logic & Dell MegaRAID SAS RAID controller SYNOPSIS
mfi* at pci? dev ? function ? DESCRIPTION
The mfi driver provides support for the MegaRAID SAS family of RAID controllers, including: - Dell PERC 5/e, PERC 5/i, PERC 6/e, PERC 6/i - Intel RAID Controller SRCSAS18E, SRCSAS144E - LSI Logic MegaRAID SAS 8208ELP, MegaRAID SAS 8208XLP, MegaRAID SAS 8300XLP, MegaRAID SAS 8308ELP, MegaRAID SAS 8344ELP, MegaRAID SAS 8408E, MegaRAID SAS 8480E, MegaRAID SAS 8708ELP, MegaRAID SAS 8888ELP, MegaRAID SAS 8880EM2, MegaRAID SAS 9260-8i - IBM ServeRAID M1015, ServeRAID M5014 These controllers support RAID 0, RAID 1, RAID 5, RAID 6, RAID 10, RAID 50 and RAID 60 using either SAS or SATA II drives. Although the controllers are actual RAID controllers, the driver makes them look just like SCSI controllers. All RAID configuration is done through the controllers' BIOSes. mfi supports monitoring of the logical disks in the controller through the bioctl(8) and envstat(8) commands. EVENTS
The mfi driver is able to send events to powerd(8) if a logical drive in the controller is not online. The state-changed event will be sent to the /etc/powerd/scripts/sensor_drive script when such condition happens. SEE ALSO
intro(4), pci(4), scsi(4), sd(4), bioctl(8), envstat(8), powerd(8) HISTORY
The mfi driver first appeared in NetBSD 4.0. BSD
March 22, 2012 BSD
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