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FAQ

From next3

Revision as of 10:13, 25 February 2010 by Amir73il (Talk | contribs)
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Contents

What is Next3?

Next3 is a flavor of the widely used Ext3 file system with built-in support for snapshots.

What does the N stand for?

Nothing.

Is Next3 a new file system?

No, Next3 was cloned from Ext3 as an independent development branch. Basically, it's Ext3 with snapshot support patches.

What is the development status of Next3?

Version 1.0.0 has been in beta testing for a while, with no serious issues found. The tests were limited to a specific hardware configuration (ARM, single code, 512MB RAM) with a specific Linux installation. Next3 will become publicly available for a wider beta soon.

Can the snapshot support be added to Ext4?

Most of the snapshot code can work on Ext4, but the move-on-write technology used for regular files data blocks is not applicable for extent mapped files.

Does Next3 change the on-disk format of Ext3?

No, it only uses some reserved fields in the super block and inode structs. Most of the snapshots data and metadata is stored in special snapshot files, which appear as regular files to Ext3 and e2fsprogs.

Can I convert an Ext3 file system to Next3?

Yes, in fact, you may mount it as Next3 without conversion and start using snapshots. However, for best performance, a patched tune2fs should be used to increase the journal size and to allocate the special "exclude" inode.

Can I convert a Next3 file system to Ext3?

When the first snapshot is taken, Next3 sets the read-only-compatible file system feature "has_snapshot", to prevent Ext3 and un-patched e2fsprogs from changing the file system without updating the snapshot. To "Convert" back to Ext3, a patched tune2fs should be used to clear the "has_snapshot" flag.

How do I read from a Next3 snapshot?

Mount the snapshot file as a read-only Ext2 file system via a loop device.

Why use Next3 and not Btrfs?

Next3 was designed to retain the proven stability of Ext3. Btrfs is a better fs, but it will take a while before it reaches the maturity level of Ext3.

Why use Next3 snapshots and not LVM snapshots?

  • Performance: small overhead per write operation (move-on-write)
  • Scalability: no extra overhead for multiple snapshots
  • Maintenance: no need to pre-allocate disk space for snapshots
  • Persistence: snapshots don't vanish when disk is full

Is Next3 related to Ext3cow?

Ext3cow is another independent project that adds continuous versioning support to Ext3. It uses a move-on-write technique similar to the one used by Next3 for regular files data blocks. Its purpose, design goals and implementation details are completely different.

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