[CentOS] BIOS RAID0 and differences between disks

Fri Nov 6 01:00:39 UTC 2020
H <agents at meddatainc.com>

On 11/04/2020 10:47 PM, Valeri Galtsev wrote:
>> On Nov 4, 2020, at 9:21 PM, John Pierce <jhn.pierce at gmail.com> wrote:
>> is it RAID 0 (striped) or raid1 (mirrored) ??
>> if you wrote on half of a raid0 stripe set, you basically trashed it.
>> blocks are striped across both drives, so like 16k on the first disk, then
>> 16k on the 2nd then 16k back on the first, repeat (replace 16k with
>> whatever your raid stripe size is).
>> if its a raid 1 mirror, then either disk by itself has the complete file
>> system on it, so you should be able to remirror the changed disk onto the
>> other drive.   you MUST do that re-mirror because your two disks are no
>> longer identical, and reads will alternate between them, so some reads will
>> get new data and others will get old data, which will be highly chaotic.
> John, I figure, BIOS RAID is essentially software RAID (handled by Linux kernel’s md module, or whatever module's name is). I have a question then. If it were RAID-1, and one of the drives was mounted, would the kernel’s md (?) module recognize that the other drive is out of sync, - there should be timestamp when each of RAID members was last in sync/used. Right? Or I am mistaken?
> If I understand correctly, OP has, or rather had (uh-huh), RAID-0.
> Valeri
> PS. I thought I was wrong, but I was mistaken ;-)
>> On Wed, Nov 4, 2020 at 6:18 PM H <agents at meddatainc.com> wrote:
>>> My computer running CentOS 7 is configured to use BIOS RAID0 and has two
>>> identical SSDs which are also encrypted. I had a crash the other day and
>>> due to a bug in the operating system update, I am unable to boot the system
>>> in RAID mode since dracut does not recognize the disks in grub. After
>>> modifying the grub command line I am able to boot the system from one of
>>> the harddisks after entering the LUKS password, seemingly without any
>>> problems but am obviously not running in RAID0 mode. When I booted in
>>> single-disk mode I am sure there were some new files created on the single
>>> SSD the system sees but I fairly quickly shut it down until this can be
>>> fixed.
>>> My question is: once the operating system fix has been released and I can
>>> once again boot in BIOS RAID0 mode and decrypting both SSDs (same password
>>> entered only once of course), how will the BIOS RAID0 react? How will it
>>> handle new files on one disk, altered timestamps etc.?
>>> Thanks.
>>> _______________________________________________
>>> CentOS mailing list
>>> CentOS at centos.org
>>> https://lists.centos.org/mailman/listinfo/centos
>> -- 
>> -john r pierce
>>  recycling used bits in santa cruz
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Gentlemen, I misspoke, it is RAID1, ie mirroring, not striping, RAID0. If it had been the latter, I would not have been able to boot from one of the two disks.

With that said, I have now rebooted my system from one disk and am making a backup to a separate harddisk using dd. I am not sure how the BIOS RAID - don't know if it is hardware or software - will handle the difference between the two disks when I am being able to reboot again once the CentOS bug has been fixed...