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Jimini
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PostPosted: Thu Feb 08, 2018 5:03 pm    Post subject: New RAID controller - drives are not recognized Reply with quote

Hey there,

I just bought a RAID controller to be able to address more drives. It is recognized as follows:
01:00.0 RAID bus controller: LSI Logic / Symbios Logic MegaRAID SAS 2108 [Liberator] (rev 05)

I do not want to use its RAID capabilities, since I am going to use mdadm to manage the array. Unfortunately, Gentoo does not recognize the drives connected to it. The controller is connectd to a backplane, which leads to the SATA disks. Since I never dealt with SAS before, I do not know if the kernel needs additional drivers or if I have to use some kind of management software.

Any help would be really appreciated.

Addendum: in the Web BIOS I can create a RAID0 for every disk - afterwards, every array / disk is recognized by Gentoo. But I am looking for a way to disable RAID functionality completely, since having to create a RAID0 for every disk at boot time would eliminate the hot swap functionality...

Addendum 2: alright, it seems as if the controller is not able to create a JBOD, which makes it pretty useless, when I want to use a software RAID.

Best regards,
Jimini
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krinn
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PostPosted: Thu Feb 08, 2018 7:31 pm    Post subject: Reply with quote

to get the drivers name, just use livecd and do lspci -k it should tell you the driver name to use.

for the drives problem, hardware raid card are not "simple controller", which generally mean, you cannot use a drive attach to it, you can only use arrays.
what's the difference? if the disk is not in an array, the disk will not be handle and will not work.

I don't really get your raid0 for every disk? You mean the card allow you to create a raid0 out of just 1 disk? Or probably more the card only allow you to create raid0 with all of them.
Some cards only offer raid0-1, some other offer more raid type, but may not show them if you lack enough drives (2 for raid 0&1, 3+ for other).
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Jaglover
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PostPosted: Thu Feb 08, 2018 7:36 pm    Post subject: Reply with quote

You need to use HBA passtrough mode to see the drives separately, I guess.
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frostschutz
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PostPosted: Thu Feb 08, 2018 10:26 pm    Post subject: Reply with quote

Some raid controllers have alternative firmware available that makes them into non-raid controllers (seems kinda pointless, but...).

If the RAID controller has on disk metadata and you learn the magic bytes that mark it "single drive raid0" (usually at end of drive), you could use an external script to prepare drives accordingly. You'd need to understand the metadata format well to safely do so.

You could get a regular controller, HBA, or try your luck with port multipliers. 5 sata port hub for $15, only SATA II though, and not every controller handles multipliers well.

sata multipliers as common as usb hubs, unfortunately that never happened so there's sata port shortage everywhere.
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szatox
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PostPosted: Fri Feb 09, 2018 9:02 pm    Post subject: Reply with quote

Quote:
You could get a regular controller, HBA, or try your luck with port multipliers. 5 sata port hub for $15, only SATA II though, and not every controller handles multipliers well.

Actually, sata port multipliers are said to totally kill performance and are be very reliable, since SATA only allows you to handle one device per controller port at any time.
You better think of them as of jukebox filled with hard drives instead of tapes.
SAS controllers on the other hand are said to handle SATA drives better than SATA controllers. They do know how to manage both, SAS and SATA, they have one-way compatible plugs and can maintain multiple sessions, so there is no additional overhead attached to like every second IO.
Unfortunately, they tend to be more expensive than 15$.

Quote:
I don't really get your raid0 for every disk? You mean the card allow you to create a raid0 out of just 1 disk?

Raid controller behaves like the bottom part of LVM. You don't have logical volumes there, but you do have physical volumes (drives) and volume groups (drives presented to the OS). You can then create partitions (logical volumes) on top of that.
Depending on your use case, you may want to manage your RAID at controller's level (stuff all the drives together into a single group), or in software (create a bunch of groups containing 1 physical drive each).
RAID0 made of a single hard drive is a simple trick that lets you expose that drive to the OS. Well, mostly. There is some metadata on the physical device. Raid controllers do write RAID configuration to the physical disks and they recognize devices tagged by them.
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Mad Merlin
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PostPosted: Thu Feb 15, 2018 11:12 pm    Post subject: Reply with quote

The 2108 is a very common chipset that ships in IR (ie, RAID) mode by default, but you can usually reflash it to IT (ie, HBA) mode: https://www.servethehome.com/lsi-sas-2108-raid-controller-information-listing/
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Jimini
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PostPosted: Wed Feb 21, 2018 5:32 am    Post subject: Reply with quote

Thank you for your very useful answers. I never worked with RAID controllers before, so I learned a lot in the last weeks.

Now I bought a used and crossflashed Dell H200, which seems to work as expected: the drives are recognized seperately AND the OS can use their full capacity of 3TB (2,7 TiB).

Best regards,
Jimini
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Mad Merlin
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PostPosted: Thu Feb 22, 2018 1:21 am    Post subject: Reply with quote

Jimini wrote:
Thank you for your very useful answers. I never worked with RAID controllers before, so I learned a lot in the last weeks.

Now I bought a used and crossflashed Dell H200, which seems to work as expected: the drives are recognized seperately AND the OS can use their full capacity of 3TB (2,7 TiB).

Best regards,
Jimini


The H200 actually uses the 2008 chipset, which is a close relative of the 2108, they differ only with respect to hardware RAID (and cost), as an HBA they are functionally identical.

Another useful link: https://www.servethehome.com/lsi-sas-2008-raid-controller-hba-information/
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Jimini
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PostPosted: Sat Apr 07, 2018 8:37 am    Post subject: Reply with quote

Mad Merlin wrote:

The H200 actually uses the 2008 chipset, which is a close relative of the 2108, they differ only with respect to hardware RAID (and cost), as an HBA they are functionally identical.

Another useful link: https://www.servethehome.com/lsi-sas-2008-raid-controller-hba-information/


Thank you for this addendum :-)

Best regards,
Jimini
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