just created raid1 on supermicro 1u w/freebsd : have ar1 ar0 ad6 ad4 options ? which is bootable

Posted on 2011-03-15
Last Modified: 2016-02-10
I just created a raid1 array using the supermicro embedded raid: now I am going to load freebsd8 on the machine and am faced with four options: ad4 ad6 ar0 and ar1: I do not know which one is bootable although I am guessing its ar0 becuase that looks like the first drive on the array?/? yes / no?? :
Question by:solunatec
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LVL 47

Expert Comment

ID: 35145749
yes the r in ar0 is for RAID.  Beware, not all raid controllers play nice with bsd.   You'll find out soon enough, however, and since there is no live data then you have no risk to just try

Author Comment

ID: 35147438
thanks..but once again I load data 'ONLY" on this raid drive..that rest gets mirrored automatically correct..?
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Accepted Solution

dlethe earned 500 total points
ID: 35147546
Yes, by using the /dev/ar0 you are telling the RAID engine to write to both physical drives.  On reads, however, it depends on the controller.  The better (i.e, expensive ones) will balance reads so that whichever disk can satisfy any pending requests the fastest gets the job of doing so.  In a perfect world, this makes reads twice as fast with RAID1 then with a non-RAID disk.

Make sure the RAID is configured so that both disks are in the boot path. Then if your primary disk fails your system will still be bootable.

Also since you are just setting it up, then I suggest doing a dry run.  Install things quickly, take the default, don't worry about setting up networking, just get it installed quickly.  Then after system si booted.  Kick off something like dd if=/dev/ar0 of=/dev/null &   

Above just reads from the raid and places in the bit bucket.   After you kick that off, remove the disk (unplug power if it is not hot swap, use proper static electricity caution).
Anyway it should stay running.

Then shutdown & reboot, and this should also be successful.  Then go through the docs, and resync that "failed" disk to make the RAID1 healthy.  

It is always good to test & familiarize yourself with disaster recovery BEFORE you have the disaster. This will likely be your only opportunity.
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Author Comment

ID: 35166222
1. when you say "it should stay running" I guess you mean the other drive should stay running and working properly? Even if the one number two drive is missing..this has only two drives.
2.should the system be able to reboot with one disk.? Adaptec Host Radi Controller only has four menu options.:a. Manage Arrays b.Create Array c.Add/Delete Hotspare d.Initialzie Drives.  Non of the sub menu options actually say resync. could it have another phrasing..: also becuase its only two drives most options arent even possible becuase I think I need another drive for it to work such as creating a Hotspare.
LVL 47

Expert Comment

ID: 35166514
1) Yes
2) yes
3) Not all controllers have a way to just select this.  Your adaptec is NOT a premium controller.  So you can accomplish this for a specific lun by using windows and telling it to chkdsk with the option  to repair bad blocks.  This forces a full check on all addressable blocks in the logical device, which is not 100% of the logical device, but as good as you can get.

Author Comment

ID: 35168389
You have more than answered my question but once more just in reference to #1. when I pulled it out I got a consistent series of 'write error' messages: I suppose this is just 'reporting' from the other drive/os of what is going on but the system would still be doing its 'other work' mail server etc...what ever its set up for???...: by the way I have looked at a few good books that tell you what things are ie. file system, network..etc....but do you know of a good book that has 'techniques' like the one you explain above..I think this would be a good sell..if it does not exist...the kind of stuff that you get in job experience....thanks again..
LVL 47

Expert Comment

ID: 35168537
Yes, you are getting the write errors because the lame firmware hasn't figured out that the disk "failed".  You can find some interesting tidbits in release notes and manuals for the controller(s) you care about, if you can get them.  But they are typically only available to developers.  Also firmware release notes help and basic online user manuals, which you should be able to get easily.

I've been in the storage biz as RAID/JBOD architect since the 90s so have had no need to READ any books, but I have taught my share of classes and have been quoted in some books, so don't keep up with what is out there :)

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