Questions tagged [copy-on-write]
The copy-on-write tag has no usage guidance.
12
questions
0
votes
2answers
700 views
Is copy-on-write not implemented based on page fault?
Operating System Concepts say
fork() we can use a technique known as copy-on-write,
which works by allowing the parent and child processes initially to share the
same pages. ...
When it is ...
1
vote
1answer
439 views
fork() and COW behavior after exec()
We understand the COW behavior after a fork (as for example described here) as follows: fork creates a copy of the parent's page table for the child and marks the physical pages read only, so if any ...
0
votes
0answers
167 views
can two running processes share the complete process image in physical memory, not just part of it?
can two running processes share the complete process image in physical memory, not just part of it?
Here I am talking about the Linux operating systems(eg. Ubuntu).
My thinking:
I think it is ...
0
votes
1answer
32 views
Report directories with contents that exist elsewhere even if scattered
I want to generate a report of directories that I know I can safely delete (even if requiring a quick manual verification), because I know that the full contents all the way down, exist elsewhere--...
0
votes
1answer
210 views
Doesn't the existence of LVM snapshots slows down writing a file system wich doesn't support them natively?
As far as understand snapshots in LVM (please, do correct me if I'm wrong): since they are not persistent and work even with a file system which doesn't itself support snapshots => I suppose it must ...
2
votes
1answer
256 views
Will writing identical data to blocks of a file under ZFS use space in snapshots?
I have a 16M file.
I take a snapshot of the ZFS filesystem which contains it.
If I overwrite the file with the same data, will ZFS need to store two copies of all of the blocks of the file?
7
votes
2answers
4k views
btrfs — Is it dangerous to defragment subvolume which has readonly snapshots?
If you open the defragment section of btrfs-filesystem(8), you will see the following ominous inscription left by the developers:
Warning: Defragmenting with Linux kernel versions < 3.9 or ≥ 3....
11
votes
4answers
6k views
Does any file system implement Copy on Write Mechanism for CP
We have seen OS doing Copy on Write optimisation when forking a process. Reason being that most of the times fork is proceeded by exec , so we don't want to incur the cost of page allocations and ...
1
vote
1answer
452 views
copy on write and read only files - linux
Suppose I have a single process which has some read-only pages, and it tries to write to one of those pages. This of course will raise a read-fault.
My question is: does linux knows that the read-...
2
votes
2answers
1k views
BTRFS inside a KVM-VM on a qcow2 formatted image
I have a Ubuntu 14.04 application appliance that makes heavy use of BTRFS snapshots. The application is meant to be hypervisor agnostic and the snapshots need to be stored with the virtual machine ...
-2
votes
1answer
328 views
How is btrfs (copy-on-write) different than RAID?
Whenever I hear copy-on-write my brain immediately starts thinking RAID. How is COW any different from RAID-x version ?
Both need more than 1 HDD to be useful, both make a copy of data when data is ...
1
vote
1answer
123 views
How can I tell which copies of a file are COW copies?
I have a ZFS system connected to a macintosh over NFS. The system is nearly full, but I have found a large number of duplicate files with jdupes.
I don't know how these copies were made, it's ...
