# Migrating CWFS

From time to time one may wish to move a CWFS instance from one device
to another.  Perhaps the old device is full or faulty.  Perhaps you'd
just like to make a backup.  In any case, the process is fairly simple.

## Prepare new device

After installing the new drive and powering up the machine, the first
thing to do is identify the new device.  The <tt>#S</tt> device
indicates that the new device has been recognised.

<pre>
cpu% ls '#S'
'#S/sdD0'
'#S/sdD1'
'#S/sdctl'
cpu%  cat '#S/sdD0/ctl'
inquiry KINGSTON SA400S37240G
config 0040 capabilities 2F00 dma 00550020 dmactl 00550020 rwm 1 rwmctl 0 lba48always off
model	KINGSTON SA400S37240G
serial	50026B768422720C
firm	SBFKJ4.3
feat	lba llba smart power nop ata8 
geometry 468862128 512
alignment 512 0
missirq	0
sloop	0
irq	18977 30
bsy	0 0
nildrive	6
part data 0 468862128
cpu% 
</pre>

Next, we prepare the MBR and DOS partition table with
<tt>disk/mbr</tt> and <tt>disk/fdisk</tt>:

<pre>
cpu% disk/mbr -m /386/mbr '#S/sdD0/data'
cpu% disk/fdisk -w -a '#S/sdD0/data'
cpu% cat '#S/sdD0/ctl'
inquiry KINGSTON SA400S37240G
config 0040 capabilities 2F00 dma 00550020 dmactl 00550020 rwm 1 rwmctl 0 lba48always off
model	KINGSTON SA400S37240G
serial	50026B768422720C
firm	SBFKJ4.3
feat	lba llba smart power nop ata8 
geometry 468862128 512
alignment 512 0
missirq	0
sloop	0
irq	20034 55
bsy	0 0
nildrive	6
part data 0 468862128
part plan9 63 468862128
cpu% 
</pre>

Now we can set up the plan9 partition table.  I've chosen to elide the
'other' partition this time around as I've never used it in the entire
6 years that I've been using the previous filesystem.

<pre>
cpu% disk/prep -w -a 9fat -a nvram -a fscache -a fsworm '#S/sdD0/plan9'
no plan9 partition table found
9fat 204800
nvram 1
fscache 78109544
fsworm 390547720
cpu% 
</pre>

## Copy old WORM

Disable the background dump service and trigger a final dump of
the old file system:

<pre>
cpu% echo startdump 0 >>/srv/cwfs.cmd
cpu% echo dump >>/srv/cwfs.cmd
</pre>

There's no point copying the entire WORM partition so let's work out
how much of it needs to be copied using the <tt>statw</tt> command:

<pre>
cpu% con -C /srv/cwfs.cmd
statw
cwstats main
	filesys main
		maddr  =        3
		msize  =     5147
		caddr  =      518
		csize  =   694845
		sbaddr =  1668338
		craddr =  1697494  1697494
		roaddr =  1697497  1697497
		fsize  =  1697599  1697599  0+48%
		slast  =           1668081
		snext  =           1697498
		wmax   =  1697497           0+48%
		wsize  =  3484185           1+ 0%
		223247 none
		  8903 dirty
		     0 dump
		461561 read
		  1134 write
		     0 dump1
		cache  5% full
</pre>

So we need only copy <tt>fsize</tt> 16K blocks.  We can use
<tt>dd(1)</tt> to do so, but **please**, double and triple check the
order of your arguments before running this command!

<pre>
cpu% dd -if '#S/sdD1/fsworm' -of '#S/sdD0/fsworm' -bs 16k -count 1697599
cpu% 
</pre>

This will likely take quite some time.  In the example above, copying
1697599*16K ≈ 25G took around 10 minutes or so.

## Bring up new FS

<pre>
cpu% bind -a '#S' /dev
cpu% cwfs64x -n newcwfs -f /dev/sdD0/fscache -C -c
config: service cwfs
config: config /dev/sdD0/fscache
config: filsys main c(/dev/sdD0/fscache)(/dev/sdD0/fsworm)
config: filsys dump o
config: recover main
config: end
checktag pc=20eb0f n(3) tag/path=Tnone/0; expected Tsuper/2
current fs is "main"
11 uids read, 7 groups used
63-bit cwfs as of Mon Nov  9 20:51:45 2020
	last boot Sat Nov 28 14:34:23 2020
cpu% 
</pre>

You can now mount the new filesystem:

<pre>
cpu% mount /srv/newcwfs /n/newroot
cpu% mount /srv/newcwfs /n/newdump dump
cpu% 
</pre>

## Copy 9fat and nvram

The last thing to do is to copy the 9fat and nvram partitions from
your old disk to the new one.  This is trivial:

<pre>
cpu% cp '#S/sdD1/9fat' '#S/sdD1/nvram' '#S/sdD0'
cpu% 
</pre>

You should now be able reboot from the new disk.