Skip to main content

linux - Understanding metadata usage behavior in a newly converted btrfs filesystem

I have a 5 TB hard drive with 3.3 TiB (as reported by du) of media files in 119k files and directories; the average file size was about 28 MiB. I converted the ext4 partition into btrfs with btrfs-convert. The process took 10.4 hours and was CPU-bound. Right after the conversion:


# btrfs fi df /mnt/btrfs/
Data, single: total=3.03TiB, used=2.21TiB
System, single: total=32.00MiB, used=236.00KiB
Metadata, single: total=1.52TiB, used=1.10TiB

btrfs allocated all space on the hard drive (3.03 + 1.52 TiB ≈ 5 TB), and it apparently put ~1 TiB of file content into metadata chunks (1.10 TiB used). This is unexpected because very few of my files would fit into the leaf nodes.


The standard solution to the huge metadata allocation is to re-balance the metadata. btrfs balance start -m took 8.0 hours and was I/O-bound. Afterwards, it appears that btrfs not only released unused metadata chunks, but also moved file content from metadata chunks into data chunks.


# btrfs fi df /mnt/btrfs/
Data, single: total=3.32TiB, used=3.31TiB
System, single: total=32.00MiB, used=104.00KiB
Metadata, single: total=3.00GiB, used=2.18GiB

Could someone explain what is happening? Why would "metadata" consume 1.10 TiB initially, and why would balancing reduce it to 2.18 GiB? Does btrfs balance move file content from metadata chunks to data chunks?


I used Linux kernel 3.13.0-46. My files have no hard links, xattrs, SELinux contexts, nor ACLs. I have not turned on compression, and have not deleted the ext4 roll back image.

Comments

Post a Comment

Popular Posts

keyboard - Is there any utility/method to change Windows key bindings to type rare chars to currently empty bindings?

I'm currently typing this post with my windows XP machine and (Spanish) keyboard, and I'd like to add some extra symbols to my text. I could open the "char map" windows utility, look for the desired symbols, and paste them. But I'd like something quickier. For example, when I'm using my OSX Mac at work, I can easily add a ©, ™, ® or similar symbols, just pressing some weird ALT-GR + G / H / J, key combinations. In my (Spanish) keyboard mapping, these combinations are empty, as they don't produce any char at all, which, on the other hand, is perfectly normal and desirable. So, I thought: Why couldn't I add some extra key mappings on top of my currently empty ALT-GR + G/J/H Keys in my Spanish keyboard, and thus, being able to quickly type these special symbols? So that's my question: Is there any utility/method to achieve that effect under windows? (My version is XP). I've even googled this for some time but no luck. I've been a long term Hot...
Post a Comment
Read more

virtualization - How to select paravirtualization interface in VirtualBox?

Given a windows 8 host system (Intel Core i5) and a Linux Fedora host, I would like to determine the optimal setting for the paravirtual interface. Options are none Default Legacy minimal Hyper-V KVM This page suggest the selection is only based on the guest system: The biggest change in VirtualBox 5.0 is the introduction of paravirtualization support, bringing higher performance and time-keeping accuracy to supported guest operating systems (Hyper-V on Windows and KVM on Linux). Is that correct? Answer The VirtualBox Manual , in the section titled Paravirtualization providers explains very clearly when each should be used (emphasis added): Minimal: Announces the presence of a virtualized environment. Additionally, reports the TSC and APIC frequency to the guest operating system. This provider is mandatory for running any Mac OS X guests. KVM: Presents a Linux KVM hypervisor interface which is recognized by Linux kernels starting with version 2.6.25. VirtualBox's implementati...
Post a Comment
Read more

Desktop reboots itself on sleep or hibernate

I have been using an ASUS M2NPV-VM motherboard for main home desktop workstation, operating Windows Vista x64. This computer has right from day one not been able to enter hibernate or standby; after Windows performs its final actions and brings the machine down, it would automatically revive itself for a reboot. Updating to the second latest BIOS (1201)has not helped (the latest BIOS revision would induce video refresh problems rendering it unusable). I have been reading related discussions on incidents similar to mine to no avail of a true workable solution. They appear to be more speculative guesses rather than actual knowledge on the inner workings of motherboard hardware. Does anybody have any electronic engineering experience on PC energy-saving standards to provide a more informed opinion how to go about getting this to work? More stories: this motherboard could not even reboot properly the first thing i used it. It was due to refresh rate of the onboard GPU, which had no influe...
Post a Comment
Read more

security - How is Linux not prone to viruses, malware and those kinds of things?

How is Linux protected against viruses? This question was a Super User Question of the Week . Read the blog entry for more details or contribute to the blog yourself Answer Well, it factually is not... it's just less subject to hackers developing viruses that target Linux systems. Consumer grade computers usually run on Windows and thus, when targeting a wide audience, Windows is the way to go. Don't misunderstand Linux and viruses, there definitely ARE Linux viruses. Some distros have additional protection layers such as SELinux (See here ) in Ubuntu for example. Then there's the default firewall and the fact that alien files don't automatically have permission to be executed. Specific execution permission has to be granted before execution is possible. (See here ) Then there are several other factors that make Linux a hard place to be for viruses usually non-root users on linux systems have no to little executable files at their disposal that would allow for virus...
Post a Comment
Read more