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# 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 `#S` device
indicates that the new device has been recognised.

	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% 

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

	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% 

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.

	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% 

## Copy old WORM

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

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

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

	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

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

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

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

	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% 

You can now mount the new filesystem:

	cpu% mount /srv/newcwfs /n/newroot
	cpu% mount /srv/newcwfs /n/newdump dump
	cpu% 

## 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:

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

You should now be able reboot from the new disk.