some questions
I am very interested in nilfs2 so I have some questions ?
1. If I understood well, nilfs is always appending to the end (is this true or is also other data modified, for example to update pointers ?). What is happening if I have deleted files and cleanerd deletes the snapshots ? Will this space be written by further write operations or will it be lost ?
2. I suppose that some fragmentation will build up, is there any defragmentation tool planned ?
3. How robust is nilfs to device errors like bad sectors ? For example if you have a disk image where bad sectors are replaced by zeros, will you still be able to recover data from other sectors ?
A message that is not in the archive (sent off-list or not yet received): 481DE17B.3080407-/[email protected]
Hi,
From: David Arendt <admin-/[email protected]>
Subject: [NILFS users] some questions
Date: Sun, 04 May 2008 18:16:59 +0200
Quoted 1 line
I am very interested in nilfs2 so I have some questions ?
Sure.
Quoted 4 lines
1. If I understood well, nilfs is always appending to the end (is this true or is also other data modified, for example to update pointers ?). What is happening if I have deleted files and cleanerd deletes the snapshots ?
If you deletes files, new directory blocks that doesn't have their entries, are just written out.
When the cleanerd finds a block that is not referred to from any snapshots, it is identified as removable and will not be copied during reclamation.
Quoted 2 lines
Will this space be written by further write operations or will it be lost ?
Eventually the abandoned block will be overrode with a new block.
(To be more exact, NILFS manages disk space with units of segments;
the cleanerd reclaims segments instead of disk blocks. )
Quoted 2 lines
2. I suppose that some fragmentation will build up, is there any defragmentation tool planned ?
The former is yes. Unfortunetely, the latter, no. Though some LFSes defrags during GC, our LFS not.
Quoted 3 lines
3. How robust is nilfs to device errors like bad sectors ? For example if you have a disk image where bad sectors are replaced by zeros, will you still be able to recover data from other sectors ?
When NILFS detects an I/O error, it tries to mark the segment including the bad block erroneous. The errorneous segment will never be reused.
Cheers,
Ryusuke Konishi
A message that is not in the archive (sent off-list or not yet received): [email protected]
Quoted 6 lines
Quoted 3 lines
3. How robust is nilfs to device errors like bad sectors ? For example if you have a disk image where bad sectors are replaced by zeros, will you still be able to recover data from other sectors ?
When NILFS detects an I/O error, it tries to mark the segment including the bad block erroneous. The errorneous segment will never be reused.
For the latter question, the current NILFS does not have this kind of data integrity.
Of course there are various opinions or ideas in the team.
I think, I'd like to make use of HW support such as SCSI DIF if Linux bio will support it.
Regards,
Ryusuke Konishi