Hi Craig, This should be my last message on this issue (I sincerely hope so as I have probably redefined the meaning of "needy") I lost the message related to the setting up of one btrfs drive and then using the force (-f) feature to get it to add the device to the array run sudo umount /dev/sdc1 prior to the force flag it was sudo umount /dev/sdb1 /dev/sdc1 then use gparted to blitz the partitions -- so only blitz /dev/sdc1 ?? but If I Recall you said the -f could be used with /dev/sdb1 live and mounted I am guessing, really, would the -f be placed here btrfs device add -f /dev/sdc1/ btrfs balance start -dconvert=raid1 -mconvert=raid1 / I am ready to jump on this if the above is correct. Many thanks Andrew On 24/2/19 11:47 am, Craig Sanders via luv-main wrote:

[ you accidentally sent this Q as private mail. replying back to the luv-main list ]

On Sun, Feb 24, 2019 at 08:33:25AM +1100, pushin.linux wrote:

...

Hi Craig,I was wondering if btrfs allows "shrinking" a patition to create free space, and if swap at the end of an SSD was better than at the start of a standard SATA drive that's the kind of question that a search engine like google or duckduckgo is good for. Also Q&A sites like https://askubuntu.com/ or https://unix.stackexchange.com/

It's been years since I used btrfs for anything real (i use ZFS), so I searched for "shrink btrfs partition" and found that it is possible. But first you need to know that resizing ANY filesystem always involves two steps: resizing the fs itself, and resizing the partition that it's on. and the order of those two steps depends on whether you are shrinking or enlarging the fs. to shrink an fs, you first shrink the fs itself and then the partition. to enlarge, you first enlarge the partition and then the fs.

For single-disk btrfs like on your root fs, it's fairly easy, just boot with the "gparted live" CD/USB[1] and tell it to resize your root btrfs partition (sda2, i think). That will resize both the fs and the partition.

For a btrfs pool with multiple partitions/disks, it's more complicated because gparted operates on individual drives so it doesn't resize all of the drives/partitions in a btrfs fs at once. You have to resize each partition in the btrfs pool separately. e.g. if you wanted to resize your /data filesystem, you'd first have to run "gparted /dev/sdb", resize sdb2, and then "gparted /dev/sdc" and be careful to change sdc2 to EXACTLY the same size as sdb1.

Personally, for a relatively trivial 4 or 8GB of swap space, i don't think it's worth the bother or the risk - messing with partitions is always a risk, it is very easy to make a mistake and that leads to data loss.

swap *IS* faster on an SSD (everything is faster on an SSD), but when you get 24GB RAM installed your system isn't going to be swapping much - it certainly won't be thrashing stuff in and out of swap and causing performance problems. swap usage will be occasional data + code that hasn't been in use for a while.

[1] https://gparted.org/

the gparted web site also has lots of useful info about partitioning and filesystems, so is a good place to learn the whys and wherefores of all this stuff.

craig

-- craig sanders <cas@taz.net.au> _______________________________________________ luv-main mailing list luv-main@luv.asn.au https://lists.luv.asn.au/cgi-bin/mailman/listinfo/luv-main