Is it safe to write files to RAID 1 Windows disks when Windows is shutdown?

3

I have created a RAID 1 (mirror) array with 2 hard drives. The RAID is built within Windows as dynamic disks; i.e., there is no hardware RAID controller. Now I need to store a backup file to one of them. Consider this scenario:

  1. Windows is shutdown
  2. System boot from USB drive
  3. A process for creating backup file initiated
  4. A file was written to one of the disks from the RAID array.

Please note that this operation is done when Windows is not running.  So here are two questions:

  1. Will this operation corrupt the RAID 1 array? If a stored file is deleted before Windows runs, will Windows see any problems/errors? Will Windows spot this operation?
  2. What will happen if Windows starts when this file is on the one of disks?

The question is mostly to try it out, but I do not have any unused drives to experiment with, and the RAID drives contain sensitive information.

OS is Windows 10. RAID is built as Windows dynamic disks.

Cherry

Posted 2017-04-21T03:06:38.280

Reputation: 797

What OS would you boot from the USB drive? Why would you follow this procedure? Personally I wouldn't risk it. Modifying a RAID volume without the proper RAID software is usually a bad idea. – Seth – 2017-04-21T05:08:09.987

1How would you even write a file to a partition without mounting it? How would you mount it without something that understands Dynamic Disks? The premise is flawed because you cannot. – Daniel B – 2017-04-21T05:15:01.090

How would you mount it without something that understands Dynamic Disks? Yes, I am using windows dynamic disks technology. The question was updated. – Cherry – 2017-04-21T15:09:09.223

Answers

1

I do not have specific Windows 10 knowledge (but have been using Software RAID arrays for a long, long time).

You definitely should not be trying to WRITING data to a disk on the array when it is not mounted - it can't end well. The data certainly won't be RAIDED when the system is restored, and will cause inconsistencies and possibly corruption.

Ignoring advanced filesystems like ZFS and BTRFS, filesystems expect to be consistent when written - and yours won't be.

Part of the problem is that the RAID array will not know what blocks have been changed - in case of where the file goes this will mean it won't be mirrored, but what would concern me more would be the divergence of information on the file allocation table or equivalent - ie the record which points to where files are.

As a best case scenario, if I were desperate (and I don't recommend you do this without a backup), I'd copy the file onto 1 disk, boot the system with only 1 disk, mark the array as bad and then rebuild it.

davidgo

Posted 2017-04-21T03:06:38.280

Reputation: 49 152

Dynamic disks are used. The question was updated. – Cherry – 2017-04-21T15:10:10.960

1@davidgo: Surely RAID drives occasionally get out of sync as a result of power failures.   Are you saying that this always results in catastrophe?   How are situations like that handled? – G-Man Says 'Reinstate Monica' – 2017-04-21T18:27:18.943

1@g-man Software raid can use a journalling system for determining what blocks have changed and rebuild consistency on loss of power - this does, however presuppose the journal is updated - when changes are made - I posit this won't be the case when bypassing RAID and writing to the disk directly. – davidgo – 2017-04-21T20:04:28.507

Asked: 2017-04-21T03:06:38.280

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Active: 2017-04-21T18:18:19.367