Opinions on Adaptec SATA HostRAID?
rogerheflin at gmail.com
Wed Mar 19 21:41:38 UTC 2008
Chris Snook wrote:
> Steve Snyder wrote:
>> On Wednesday 19 March 2008 2:53:53 pm Chris Snook wrote:
>>> Steve Snyder wrote:
>>>> I'm thinking of using the embedded Adaptec SATA HostRAID
>>>> functionality on my Supermicro X7DWA-N motherboard.
>>>> Does anyone have any experience using Adaptec's HostRAID with Fedora
>>>> 7/8/9? Any success or horror stories to relate?
>>>> Any information would be appreciated.
>>> HostRAID is just software RAID implemented in a device driver. It was
>>> originally intended for use with operating systems that lack a generic
>>> software RAID implementation. Since Linux has a robust and
>>> well-optimized generic software RAID implementation (two of them,
>>> actually), it's rather silly to use HostRAID under Linux.
>> Thanks for the info, Chris.
>> I'm a total RAID newbie and thought that the HostRAID BIOS support and
>> Linux device driver worked together, rather than being redundant.
> That's not entirely false. Recent device mapper will attempt to detect
> a HostRAID configuration and emulate it with dm-raid, but this isn't
> foolproof, and offers no benefit over simply configuring dm-raid
> directly. If you want to use mdadm for software RAID, you should
> definitely disable HostRAID entirely, as it will only cause problems.
And note that if you don't disable it and use the disks without hostraid or
dmraid, months from now on a reboot the bios might mention that it thinks the
array is out of sync, and ask if you want to fix it, if you say yes - your data
could be gone, depending on exactly what configuration you had on the disks. I
had a customer that did a reinstall without the hostraid driver (before dmraid
supported it) saw 2 disks, and used both, and months later the bios mentioned
out-of-sync and the customer allowed it to correct the "problem".
> Before you ask, I have no recommendations regarding dm-raid vs. mdadm.
> Both generally work fine. dm-raid is newer and shinier, while mdadm is
> more established and better documented.
> -- Chris
dm-raid working with the bios should be easier on a primary disk failure, but is
newer and probably also has more bugs so that may offset that ability.
mdadm does work well but on a bad failure you need the ability to understand
what happened to understand how to best fix it. I generally use mdadm because
of the more established and better documented, and I expect to be able to figure
out exactly how to fix it without data loss. And mdadm disks can be moved to
any linux machine that can support those disks and be expected to work, were the
HostRAID disks may have to be moved to another similar HostRAID machine to be
readable, so if you have a MB failure, mdadm has more options.
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