HowTO: Btrfs Root Installation

[ibuclaw]

here is a patch for fsck at boot time, because -a option is missing.
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=567681

OK, I've had a look, and the patch is absolutely horrible (in my option).
I've included it anyway, but I may change it to something proper if I get time.

Regards

[degarb]

I could not get compression to work.

anyone up to writing a real manual for newbies to get seamless compression.

Like what to add to fstab, how , and how to find out what.

How to keep the os from mounting before you do a mount o compress.

I got mkfs to work and files to load. but not to compress. I added a gig to two gig drive and was left with a gig free. I am assuming it didn't work.

[ibuclaw]

I could not get compression to work.

anyone up to writing a real manual for newbies to get seamless compression.

Like what to add to fstab, how , and how to find out what.

How to keep the os from mounting before you do a mount o compress.

I got mkfs to work and files to load. but not to compress. I added a gig to two gig drive and was left with a gig free. I am assuming it didn't work.

Put "compress" as an option in fstab.

There are some caveats with btrfs compression, now in the guide, that I have not mentioned prior, and if a file doesn't seem to compress, then the file system is only working to design.

Regards
Iain

[degarb]

Put "compress" as an option in fstab.

There are some caveats with btrfs compression, now in the guide, that I have not mentioned prior, and if a file doesn't seem to compress, then the file system is only working to design.

Regards
Iain

I hit mount I can see my external usb drive on sdb1

Thanks. Unfortunately, when I do blkid -o value -s UUID /dev/sdb1

or even

blkid -o value -s UUID /dev/sdb1


Nothing is printed out, nor is there any naturally occuring fstab reference to sdb anywhere. there is a natural reference to the internal drive sda1 and the swap sda5.

All i am interested in is seemlilessly (invisible to apps) compressing a drive or folder, like ntfs. Little reference to it. You refer to compress 0 in fstab, but why not compress 9. I also wonder about spacing in this.

[degarb]

maybe blkid doesn't work with usb devices so the compression wont work on external drives?

[ibuclaw]

All i am interested in is seemlilessly (invisible to apps) compressing a drive or folder, like ntfs. Little reference to it. You refer to compress 0 in fstab, but why not compress 9. I also wonder about spacing in this.

There is no level of compression in btrfs, only compress, or no compress. You are confusing the 4th column with the 5th column of the fstab line.

maybe blkid doesn't work with usb devices so the compression wont work on external drives?

try:

sudo blkid /dev/sdb1

No fancy options. You should see 'UUID=1234-5678' outputted somewhere.

Regards
Iain

[jdong]

There is no level of compression in btrfs, only compress, or no compress. You are confusing the 4th column with the 5th column of the fstab line.


try:

sudo blkid /dev/sdb1

No fancy options. You should see 'UUID=1234-5678' outputted somewhere.

Regards
Iain

To clarify, nowadays in btrfs there are two compress methods:

-o compress: Smart compression -- compress highly compressible files, but back off and blacklist incompressible content.

-o compress_force: Forced compression. Even at horrendous cost to performance, apply compression.


Both algorithms use zlib (gzip) compression at default level -- this is not tunable yet.

[degarb]

To clarify, nowadays in btrfs there are two compress methods:

-o compress: Smart compression -- compress highly compressible files, but back off and blacklist incompressible content.

-o compress_force: Forced compression. Even at horrendous cost to performance, apply compression.


Both algorithms use zlib (gzip) compression at default level -- this is not tunable yet.

These are for manually mounting. what would the fstab equivalent be?

[ibuclaw]

These are for manually mounting. what would the fstab equivalent be?

Just add "compress" or "compress_force" (thank-you again jdong for further enlightenment) in the 4th column of your fstab file.

This is outlined in the guide under "Compression and other Mount Options"

Regards
Iain

[degarb]

I am fuzzy on what happens to file sizes and readability when you mount/toggle compression.

I seem to be thinking/assuming: if off, new files aren't compressed, when mounted on, then new files are written with compress but old files will be not be compressed. Now if toggled off, are these compressed files readable and transparently working? But what about files the a vdi that "grows" if you create it in compressed drive, the turn off compression, when it grows does it just go to large size?