Re: Question about Running rsnapshot

[Andrew McGlashan]

Hi,

On 05/05/18 07:45, Martin McCormick wrote:
>   I just realized that I goofed when I wrote the name of
> the application that combines multiple drives in to one large
> drive.  I meant
> mhddfs for example:
> mhddfs /rsnapshot1,/rsnapshot2 /var/cache/rsnapshot -o mlimit=100M 
> >/dev/null 2>&1 

Okay, that explains it.  It seems that the underlying file systems are
independent from each other in most respects.  The virtual presentation
is, interesting, but I wouldn't be using this setup for backups even
though it might be useful for other types of use.


https://romanrm.net/mhddfs

Cheers
A.



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Re: Question about Running rsnapshot

[Eduardo M KALINOWSKI]

On 04-05-2018 16:52, Martin McCormick wrote:
> The backup file system resides on a pair of 256 GB usb
> drives which are ganged together in to 1 large drive using mmddfs

You can't have a hard link between files in different drives[0]. mmddfs
is probably copying instead of linking, even if it receives a ln call,
when it determines that each file must end up in different disks.

For your use case, LVM seems more adequate: you'll have only one
filesystem, even if at disk level it's stored in two disks.


[0]Actually, they must be in the same filesystem

-- 
Eduardo M KALINOWSKI
edua...@kalinowski.com.br

Re: Question about Running rsnapshot

[Martin McCormick]

I am replying to two messages at once.

Andrew McGlashan  writes:
> Is it this:
> 
> https://www.microchip.com/SWLibraryWeb/product.aspx?product=Memory%20Disk%20Drive%20File%20System
> 
> 

I just realized that I goofed when I wrote the name of
the application that combines multiple drives in to one large
drive.  I meant
mhddfs for example:
mhddfs /rsnapshot1,/rsnapshot2 /var/cache/rsnapshot -o mlimit=100M 
>/dev/null 2>&1 

The file systems used on these drives are Linux file systems and
are mounted ext4.
Greg Wooledge  writes:
> Two (or more) hardlinks to the same file can only exist within a file
> system.  If /a and /b are separate file systems, then it is completely
> impossible for /a/file and /b/file to be hardlinks to each other.

That's what confuses me right now as this obviously works as I
can go to all of those backup directories and cat that file or
any of the several thousand other files in the backup and read
their contents.

I had a look at rsnapshot which is a perl script and the
line that makes the link is:

print_cmd("ln $srcpath $destpath");

Maybe I am confused about what produces a hard link but I thought
that did.  It ends up looking like all the blocks of that file
are in that directory when in fact we are reading blocks that
were only written once and only seem to be in multiple file
systems.

Martin

Re: Question about Running rsnapshot

[Andrew McGlashan]

On 05/05/18 05:52, Martin McCormick wrote:
> Andrew McGlashan  writes:
>> Have you got your backup areas on different file systems?
> 
> I do.  The backup file system resides on a pair of 256 GB usb
> drives which are ganged together in to 1 large drive using mmddfs

Is it this:

https://www.microchip.com/SWLibraryWeb/product.aspx?product=Memory%20Disk%20Drive%20File%20System



If so, that looks like it is a FAT type file system and that doesn't
have the inodes like ext4 (and similar) has.

A.

Re: Question about Running rsnapshot

[Greg Wooledge]

On Fri, May 04, 2018 at 02:52:05PM -0500, Martin McCormick wrote:
>   As I write this, I am beginning to realize that maybe only
> hard links in the same directory structure will reference the
> same inode and that hard links spanning multiple directory trees
> can be different but contain metadata that copy the map of the
> original file which was the one that was on inode 16.

Two (or more) hardlinks to the same file can only exist within a file
system.  If /a and /b are separate file systems, then it is completely
impossible for /a/file and /b/file to be hardlinks to each other.

Re: Question about Running rsnapshot

[Martin McCormick]

Andrew McGlashan  writes:
> Hi,
> 
> Have you got your backup areas on different file systems?

I do.  The backup file system resides on a pair of 256 GB usb
drives which are ganged together in to 1 large drive using mmddfs
and then mounted on /var/cache/rsnapshot.  The very first backup
I took was the full backup and that particular file showed an
inode number of 16.  The remaining two backups are halfday.0 and
halfday.1.  Each of those files has a working version of that
same file and one has an inode number of 11 while the other has
an inode number of 6.  Each of these backups is a different tree
with the vast majority of files being hard links to the first
backup which copied the contents of the working drive to the
backup drive.

As I write this, I am beginning to realize that maybe only
hard links in the same directory structure will reference the
same inode and that hard links spanning multiple directory trees
can be different but contain metadata that copy the map of the
original file which was the one that was on inode 16.

If that is correct, then thank you for helping my slow
mind to think since I was confused and expected all the hard
links to have an inode of 16.

The purpose behind this exercise is to make sure that the
backups I am creating are good as the first or full backup used
about 25% of the total space and the other two backups hardly
added any more space.  I was able to read the contents of the
file on each of the subsequent two backups so it definitely is
working.

Martin McCormick

Re: Question about Running rsnapshot

[Andrew McGlashan]

Hi,

On 05/05/18 03:40, Martin McCormick wrote:
> rsnapshot hard-links files that haven't changed to save space.  I
> am doing two half-day backups and a daily each day.  Shouldn't
> the inode number as in ls -i filename stay the same for all the
> backups?  There is a daily.0 file plus a halfday.0 and a
> halfday.1 backup and all 3 have different inode numbers for the
> same file which hasn't changed since 2008.  Doing ls -l on that
> file does show 3 links to it.  On the working drive, there is
> only 1 which is what it should be.

Have you got your backup areas on different file systems?

4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
daily.0/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
daily.1/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
daily.2/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
daily.3/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
daily.4/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
daily.5/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
daily.6/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.0/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.10/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.11/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.12/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.13/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.14/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.15/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.1/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.2/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.3/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.4/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.5/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.6/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.7/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.8/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
hourly.9/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
monthly.0/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
monthly.1/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
monthly.2/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
monthly.3/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
monthly.4/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
monthly.5/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
monthly.6/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
monthly.7/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
monthly.8/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
weekly.0/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
weekly.1/server/root/etc/passwd
4720525 -rw-r--r-- 35 root root 1226 Oct 12  2016
weekly.2/server/root/etc/passwd



Cheers
A.

Question about Running rsnapshot

[Martin McCormick]

rsnapshot hard-links files that haven't changed to save space.  I
am doing two half-day backups and a daily each day.  Shouldn't
the inode number as in ls -i filename stay the same for all the
backups?  There is a daily.0 file plus a halfday.0 and a
halfday.1 backup and all 3 have different inode numbers for the
same file which hasn't changed since 2008.  Doing ls -l on that
file does show 3 links to it.  On the working drive, there is
only 1 which is what it should be.

Today, daily.0 represents the full backup of the system
and daily.1 tomorrow will be a renamed version of today's daily.0
directory.  df -h looks good in that disk usage appears to be the
equivalent of one full backup even with 3 intervals of backup now
so I am curious as to why the inode numbers for hard links to the
same file are different.

Thanks.

Martin McCormick