Re: Accessing discs connected to H/W RAID controller over SG interface

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On Mon, 12 Feb 2024, Tom Crane wrote:

We have a system whose RAID array has performance problems. We see I/O maxing out at throughputs far below the spec of the controller and even well below that of individual discs attached to it.

The RAID controller from Areca is configured with 2-off RAID volumes and has 4-off 6TB discs attached to it. I would like to be able to access the 4 discs individually, e.g. to be able to dd them to /dev/null to check on their performances. I know we could JBOD the discs and do S/W RAID but this is a production system and in any case the point of having a H/W RAID controller is to avoid this!

This shows the configuration,

# lsscsi -gs
[0:0:0:0] disk Areca ARC-1226-VOL#000 R001 /dev/sda /dev/sg0 199GB [0:0:0:1] disk Areca ARC-1226-VOL#001 R001 /dev/sdb /dev/sg1 11.8TB [0:0:16:0] process Areca RAID controller R001 - /dev/sg2 -

I know that some access to the individual discs attached is possible because the smartmontools utility smartctl can do it, e.g.,

# smartctl -i -d areca,1 /dev/sg2
smartctl 7.0 2018-12-30 r4883 [x86_64-linux-3.10.0-1160.80.1.el7.x86_64] (local build)
Copyright (C) 2002-18, Bruce Allen, Christian Franke,

Model Family:     Western Digital Red
Device Model:     WDC WD60EFRX-68L0BN1

I was hoping to use 'sg_dd if=<???> of=/dev/null' or similar. I could not find what I was looking for at or elsewhere. Is this possible? Can anyone give me some pointers?

Many thanks
Tom Crane>

I have not yet had any follow-up to my query above. Would anyone be kind enought to give me some comment/pointers?

If there is a more appropriate forum for my query or if the information I am looking for is documented somewhere, could someone point me to it?

Tom Crane

Tom Crane, Digital Electronics Engineer, Dept. Physics, Royal Holloway, University of London, Egham Hill,
Egham, Surrey, TW20 0EX, England.
Email:  T.Crane@xxxxxxxxxx

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