4 ms·

Hell, there's XFS if you love stability but want CoW.

josephcsible 1y ago
XFS doesn't support whole-volume snapshots, which is the main reason I want CoW filesystems. And it also stands out as being basically the only filesystem that you can't arbitrarily shrink without needing to wipe and reformat.
- leogao 1y ago
  you can always have an LVM layer for atomic snapshots
  - josephcsible 1y ago
    There are advantages to having the filesystem do the snapshots itself. For example, if you have a really big file that you keep deleting and restoring from a snapshot, you'll only pay the cost of the space once with Btrfs, but will pay it every time over with LVM.
  - shtripok 1y ago
    On some of my zfs servers, the number of snapshots (mostly periodic, rotated — hour, day, month, updates, data maintenance work) is 10-12 thousand. LVM can't do that.
- kzrdude 1y ago
  there was the "old dog new tricks" xfs talk long time ago, but I suppose it was for fun and exploration and not really a sneak peek into snapshots
- MertsA 1y ago
  You can shrink XFS, but only the realtime volume. All you need is xfs_db and a steady hand. I once had to pull this off for a shortened test program for a new server platform at Meta. Works great except some of those filesystems did somehow get this weird corruption around used space tracking that xfs_repair couldn't detect... It was mostly fine.
- adrian_b 1y ago
  Many years ago, XFS did not support snapshots. However, there is also a long time since XFS supports snapshots. See for example: https://thelinuxcode.com/xfs-snapshot/ https://thelinuxcode.com/xfs-snapshot/ I am not sure what you mean by "whole-volume" snapshots, but I have not noticed any restrictions in the use of the XFS snapshots. As expected, they store a snapshot of the entire file system, which can be restored later. In many decades of managing computers with all kinds of operating systems and file systems, on a variety of servers and personal computers, I have never had the need to shrink a file system. I cannot imagine how such a need can arise, except perhaps as a consequence of bad planning. There are also many decades since I have deprecated the use of multiple partitions on a storage device, with the exception of bootable devices, which must have a dedicated partition for booting, conforming to the BIOS or UEFI expectations. For anything that was done in the ancient times with multiple partitions there are better alternatives now. With the exception of bootable USB sticks with live Linux or FreeBSD partitions, I use XFS on whole SSDs or HDDs (i.e. unpartitioned), regardless if they are internal or external, so there is never any need for changing the size of the file system. Even so, copying a file system to an external device, reformatting the device and copying the file system back is not likely to be significantly slower than shrinking in place. In fact sometimes it can be faster and it has the additional benefit that the new copy of the file system will be defragmented. Much more significant than the lack of shrinking ability, which may slow down a little something that occurs very seldom, is that both EXT4 and XFS are much faster for most applications than the other file systems available for Linux, so they are fast for the frequent operations. You may choose another file system for other reasons, but choosing it for making faster a very rare operation like shrinking is a very weak reason.
  - CoolCold 1y ago
    I definitely met several cases where support for shrinking would be beneficial - usually something about migrations and things like that, but yet I agree it's quite rare operation. Benefits come with lower amount of downtime window and/or expenses in time and duplicating systems. I.e. back in ~ 2013-2014 while moving some baremetal Windows server into VMware, srhinking and then optimizing MFT helped to save AFAIR 2 hours of downtime window. > except perhaps as a consequence of bad planning Assuming people go to Clouds instead of physical servers because they may need to add 100 more nodes "suddenly" - selling point of Clouds is "avoid planning" - one may expect cases of need of shrinking are rising, now lowing. It may be mitigated by different approaches of course - i.e. often it's easier to resetup VM, but yet.

XFS doesn't support whole-volume snapshots, which is the main reason I want CoW filesystems. And it also stands out as being basically the only filesystem that you can't arbitrarily shrink without needing to wipe and reformat.

leogao 1y ago
you can always have an LVM layer for atomic snapshots
- josephcsible 1y ago
  There are advantages to having the filesystem do the snapshots itself. For example, if you have a really big file that you keep deleting and restoring from a snapshot, you'll only pay the cost of the space once with Btrfs, but will pay it every time over with LVM.
- shtripok 1y ago
  On some of my zfs servers, the number of snapshots (mostly periodic, rotated — hour, day, month, updates, data maintenance work) is 10-12 thousand. LVM can't do that.
kzrdude 1y ago
there was the "old dog new tricks" xfs talk long time ago, but I suppose it was for fun and exploration and not really a sneak peek into snapshots
MertsA 1y ago
You can shrink XFS, but only the realtime volume. All you need is xfs_db and a steady hand. I once had to pull this off for a shortened test program for a new server platform at Meta. Works great except some of those filesystems did somehow get this weird corruption around used space tracking that xfs_repair couldn't detect... It was mostly fine.
adrian_b 1y ago
Many years ago, XFS did not support snapshots. However, there is also a long time since XFS supports snapshots. See for example: https://thelinuxcode.com/xfs-snapshot/ https://thelinuxcode.com/xfs-snapshot/ I am not sure what you mean by "whole-volume" snapshots, but I have not noticed any restrictions in the use of the XFS snapshots. As expected, they store a snapshot of the entire file system, which can be restored later. In many decades of managing computers with all kinds of operating systems and file systems, on a variety of servers and personal computers, I have never had the need to shrink a file system. I cannot imagine how such a need can arise, except perhaps as a consequence of bad planning. There are also many decades since I have deprecated the use of multiple partitions on a storage device, with the exception of bootable devices, which must have a dedicated partition for booting, conforming to the BIOS or UEFI expectations. For anything that was done in the ancient times with multiple partitions there are better alternatives now. With the exception of bootable USB sticks with live Linux or FreeBSD partitions, I use XFS on whole SSDs or HDDs (i.e. unpartitioned), regardless if they are internal or external, so there is never any need for changing the size of the file system. Even so, copying a file system to an external device, reformatting the device and copying the file system back is not likely to be significantly slower than shrinking in place. In fact sometimes it can be faster and it has the additional benefit that the new copy of the file system will be defragmented. Much more significant than the lack of shrinking ability, which may slow down a little something that occurs very seldom, is that both EXT4 and XFS are much faster for most applications than the other file systems available for Linux, so they are fast for the frequent operations. You may choose another file system for other reasons, but choosing it for making faster a very rare operation like shrinking is a very weak reason.
- CoolCold 1y ago
  I definitely met several cases where support for shrinking would be beneficial - usually something about migrations and things like that, but yet I agree it's quite rare operation. Benefits come with lower amount of downtime window and/or expenses in time and duplicating systems. I.e. back in ~ 2013-2014 while moving some baremetal Windows server into VMware, srhinking and then optimizing MFT helped to save AFAIR 2 hours of downtime window. > except perhaps as a consequence of bad planning Assuming people go to Clouds instead of physical servers because they may need to add 100 more nodes "suddenly" - selling point of Clouds is "avoid planning" - one may expect cases of need of shrinking are rising, now lowing. It may be mitigated by different approaches of course - i.e. often it's easier to resetup VM, but yet.