kern/143056: [ata] atacontrol(8) can not create raid1 (mirror) from one drive

Oles Hnatkevych don_oles at
Sun Jan 24 11:50:04 UTC 2010

The following reply was made to PR kern/143056; it has been noted by GNATS.

From: Oles Hnatkevych <don_oles at>
To: bug-followup at, don_oles at
Subject: Re: kern/143056: [ata] atacontrol(8) can not create raid1 (mirror)
 from one drive
Date: Sun, 24 Jan 2010 13:49:13 +0200

 How I can persuade people that there's no anything in any religion 
 against creating degraded mirrors from one hard drive, since it is
 1) technically possible
 2) it is very helpful
 Let's change the documentation and fix the religious problem.
 Example 1:
 The 300GB mirror is broken on a production system. But the space is 
 scarce, the decision is to migrate to 500 GB mirror. Two 500G disks are 
 Intended (unsupported) way:
 The 500GB disk is inserted, from it created a one-disk mirror, mirror is 
 sliced and configured to boot, with rsync the whole system is migrated 
 from one degraded mirror to another, then again in single-user mode, 
 server turned off , 300 Gb disk taken out, both 500 Gb disks inserted, 
 server booted from a degraded 500G mirror, second disk added to mirror.
 The way I had to go:
 The same but I had to find a separate box in which I inserted both 500G 
 drives, boot from freebsd dvd in fixit mode, create full mirror, take 
 one hard drive, boot again and remove degraded mirror from second hard 
 drive (to add it later, not to confuse the production server).
 Example 2:
 I want to have a mirror but right now only one hard drive is available, 
 but I know that in month or two I'll have money to buy another one. It's 
 much more convenient to setup system on one-drive-mirror and then add 
 another one than to mess around with migration from single-drive without 
 mirror to a full mirror. Much more.
 Gmirror already supports one-drive mirrors. Yes, its author is more 
 Oles Hnatkevych
 Skype: don_oles
 Email/Jabber: don_oles at

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