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Full Discussion: Software RAID on Linux
Operating Systems Linux Software RAID on Linux Post 302283085 by otheus on Monday 2nd of February 2009 01:59:34 PM
Old 02-02-2009
That's a good point about Sata throughput and drive throughput. What you must consider, however, is that RAID tries to write 5 blocks to five different drives right after another. Each contoller gets the data, sends a write request, waits for it to finish, sends the next, etc. Each drive gets the SATA command, positions the head to the correct place, then writes the data. When done serially, this process can reduce your throughput from 90 MB/s to 18 MB/s (90/5).

Since the PCI bus is much faster than the SATA bus, the OS can send the data to multiple controllers by the time the first disk is about to write. Thus, the OS can take advantage of multiple SATA controllers. (It could be that some SATA PCI controllers have multiple busses and multiple drive controllers, which would be nice). But if you're fine with the 20 MB/s, then just a single controller is fine.

As far as partitions, leave /boot, /, and /usr on your 80 GB drive. I don't know why you need to separate /tmp from / unless you have a large need for /tmp space (which is very uncommon these days -- most programs use the current working directory for scratch space). If you have a need for /tmp, but that consists of lots of small data files, use a memory-based solution.

You almost won't need swap at all with 4+ GB. If you have one, keep it on the array, but not on the slower 80 gb drive.
 

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AMR(4)							   BSD Kernel Interfaces Manual 						    AMR(4)

NAME
amr -- MegaRAID SCSI/ATA/SATA RAID driver SYNOPSIS
To compile this driver into the kernel, place the following lines in your kernel configuration file: device pci device scbus device amr Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5): amr_load="YES" DESCRIPTION
The amr driver provides support for LSI Logic MegaRAID SCSI, ATA and SATA RAID controllers and legacy American Megatrends MegaRAID SCSI RAID controllers, including models relabeled and sold by Dell and Hewlett-Packard. LSI MegaRAID SAS controllers are supported by mfi(4) and will not work with this driver. HARDWARE
Controllers supported by the amr driver include: o MegaRAID SATA 150-4 o MegaRAID SATA 150-6 o MegaRAID SATA 300-4X o MegaRAID SATA 300-8X o MegaRAID SCSI 320-1E o MegaRAID SCSI 320-2E o MegaRAID SCSI 320-4E o MegaRAID SCSI 320-0X o MegaRAID SCSI 320-2X o MegaRAID SCSI 320-4X o MegaRAID SCSI 320-0 o MegaRAID SCSI 320-1 o MegaRAID SCSI 320-2 o MegaRAID SCSI 320-4 o MegaRAID Series 418 o MegaRAID i4 133 RAID o MegaRAID Elite 1500 (Series 467) o MegaRAID Elite 1600 (Series 493) o MegaRAID Elite 1650 (Series 4xx) o MegaRAID Enterprise 1200 (Series 428) o MegaRAID Enterprise 1300 (Series 434) o MegaRAID Enterprise 1400 (Series 438) o MegaRAID Enterprise 1500 (Series 467) o MegaRAID Enterprise 1600 (Series 471) o MegaRAID Express 100 (Series 466WS) o MegaRAID Express 200 (Series 466) o MegaRAID Express 300 (Series 490) o MegaRAID Express 500 (Series 475) o Dell PERC o Dell PERC 2/SC o Dell PERC 2/DC o Dell PERC 3/DCL o Dell PERC 3/QC o Dell PERC 4/DC o Dell PERC 4/IM o Dell PERC 4/SC o Dell PERC 4/Di o Dell PERC 4e/DC o Dell PERC 4e/Di o Dell PERC 4e/Si o Dell PERC 4ei o HP NetRAID-1/Si o HP NetRAID-3/Si (D4943A) o HP Embedded NetRAID o Intel RAID Controller SRCS16 o Intel RAID Controller SRCU42X DIAGNOSTICS
Driver initialisation/shutdown phase amr%d: memory window not available amr%d: I/O window not available The PCI BIOS did not allocate resources necessary for the correct operation of the controller. The driver cannot attach to this controller. amr%d: busmaster bit not set, enabling The PCI BIOS did not enable busmaster DMA, which is required for the correct operation of the controller. The driver has enabled this bit and initialisation will proceed. amr%d: can't allocate register window amr%d: can't allocate interrupt amr%d: can't set up interrupt amr%d: can't allocate parent DMA tag amr%d: can't allocate buffer DMA tag amr%d: can't allocate scatter/gather DMA tag amr%d: can't allocate s/g table amr%d: can't allocate mailbox tag amr%d: can't allocate mailbox memory A resource allocation error occurred while initialising the driver; initialisation has failed and the driver will not attach to this con- troller. amr%d: can't obtain configuration data from controller amr%d: can't obtain product data from controller The driver was unable to obtain vital configuration data from the controller. Initialisation has failed and the driver will not attach to this controller. amr%d: can't establish configuration hook amr%d: can't scan controller for drives The scan for logical drives managed by the controller failed. No drives will be attached. amr%d: device_add_child failed amr%d: bus_generic_attach returned %d Creation of the logical drive instances failed; attachment of one or more logical drives may have been aborted. amr%d: flushing cache... The controller cache is being flushed prior to shutdown or detach. Operational diagnostics amr%d: I/O beyond end of unit (%u,%d > %u) A partitioning error or disk corruption has caused an I/O request beyond the end of the logical drive. This may also occur if FlexRAID Vir- tual Sizing is enabled and an I/O operation is attempted on a portion of the virtual drive beyond the actual capacity available. amr%d: polled command timeout An initialisation command timed out. The initialisation process may fail as a result. amr%d: bad slot %d completed The controller reported completion of a command that the driver did not issue. This may result in data corruption, and suggests a hardware or firmware problem with the system or controller. amr%d: I/O error - %x An I/O error has occurred. SEE ALSO
cd(4), da(4), mfi(4), sa(4), scsi(4) AUTHORS
The amr driver was written by Mike Smith <msmith@FreeBSD.org>. This manual page was written by Mike Smith <msmith@FreeBSD.org> and Jeroen Ruigrok van der Werven <asmodai@FreeBSD.org>. BSD
March 29, 2006 BSD
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