With respect to XFS Bitmap flush to disk

With respect to XFS Bitmap flush to disk

[Halsey Pian]

Dear All,

Recently, I try to read analyze the bitmap of XFS file system, it seems that I cannot read the latest bitmap from hard disk involving the XFS, and cannot read the accurate info even after a long time. For example, i cannot get the relevant bitmap info after I add/delete a big file to/from XFS file system.

I tried several solution, and find it out that I must execute xfs_freeze for the XFS partition in CentOS7, and it seems that xfs_freeze doesn’t work for XFS version included in Redhat6.5, I must umount/mount the xfs, then I can get the latest bitmap info related to the latest data located in disk.

What  strategy does XFS use to cache/flush bitmap to hard disk?  How can I get the accurate bitmap info especially for Redhat6 series Operating System? Could you please give help on it?

Thanks in advance! ☺




Halsey Pian 

Re: With respect to XFS Bitmap flush to disk

[Stefan Ring]

On Mon, Feb 27, 2017 at 3:11 AM, Halsey Pian <halsey.pian@gmail.com> wrote:
>
> I tried several solution, and find it out that I must execute xfs_freeze for the XFS partition in CentOS7, and it seems that xfs_freeze doesn’t work for XFS version included in Redhat6.5, I must umount/mount the xfs, then I can get the latest bitmap info related to the latest data located in disk.

Why do you think that xfs_freeze does not work on el6?

Re: With respect to XFS Bitmap flush to disk

[Eric Sandeen]

On 2/26/17 8:11 PM, Halsey Pian wrote:
> Dear All,
> 
> Recently, I try to read analyze the bitmap of XFS file system, it
> seems that I cannot read the latest bitmap from hard disk involving
> the XFS, and cannot read the accurate info even after a long time.
> For example, i cannot get the relevant bitmap info after I add/delete
> a big file to/from XFS file system.

In general, attempting to read metadata from a mounted block device
isn't going to be reliable.  For one, changes may only be staged
in the log, and not yet in their final disk location.
 
> I tried several solution, and find it out that I must execute
> xfs_freeze for the XFS partition in CentOS7, and it seems that
> xfs_freeze doesn’t work for XFS version included in Redhat6.5, I must
> umount/mount the xfs, then I can get the latest bitmap info related
> to the latest data located in disk.
> 
> What  strategy does XFS use to cache/flush bitmap to hard disk?  How
> can I get the accurate bitmap info especially for Redhat6 series
> Operating System? Could you please give help on it?

The short answer is "you can't."  Directly reading the block device
while mounted isn't a supported use of the filesystem.

What are you trying to do, here?

Thanks,
-Eric

> Thanks in advance! ☺
> 
> 
> 
> 
> Halsey Pian
> 
> 
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