mtime, ctime, and atime
Unix keeps 3 timestamps for each file: mtime, ctime, and atime. Most people seem to understand atime (access time), it is when the file was last read. There does seem to be some confusion between mtime and ctime though. ctime is the inode change time while mtime is the file modification time. “Change” and “modification” are pretty much synonymous. There is no clue to be had by pondering those words. Instead you need to focus on what is being changed. mtime changes when you write to the file. It is the age of the data in the file. Whenever mtime changes, so does ctime. But ctime changes a few extra times. For example, it will change if you change the owner or the permissions on the file.

Let’s look at a concrete example. We run a package called Samba that lets PC’s access files. To change the Samba configuration, I just edit a file called smb.conf. (This changes mtime and ctime.) I don’t need to take any other action to tell Samba that I changed that file. Every now and then Samba looks at the mtime on the file. If the mtime has changed, Samba rereads the file. Later that night our backup system runs. It uses ctime, which also changed so it backs up the file. But let’s say that a couple of days later I notice that the permissions on smb.conf are 666. That’s not good..anyone can edit the file. So I do a “chmod 644 smb.conf”. This changes only ctime. Samba will not reread the file. But later that night, our backup program notices that ctime has changes, so it backs up the file. That way, if we lose the system and need to reload our backups, we get the new improved permission setting.

Here is a second example. Let’s say that you have a data file called employees.txt which is a list of employees. And you have a program to print it out. The program not only prints the data, but it obtains the mtime and prints that too. Now someone has requested an employee list from the end of the year 2000 and you found a backup tape that has that file. Many restore programs will restore the mtime as well. When you run that program it will print an mtime from the end of the year 2000. But the ctime is today. So again, our backup program will see the file as needing to be backed up.

Suppose your restore program did not restore the mtime. You don’t want your program to print today’s date. Well no problem. mtime is under your control. You can set it to what ever you want. So just do:
$ touch -t 200012311800 employees.txt
This will set mtime back to the date you want and it sets ctime to now. You have complete control over mtime, but the system stays in control of ctime. So mtime is a little bit like the date on a letter while ctime is like the postmark on the envelope.

==========================

find command -mtime -ctime -atime
The find command uses arguments like:
-mtime -2
-mtime +2
-mtime 2

There are -ctime and -atime options as well. Since we now understand the differences among mtime, ctime, and atime, by understanding how find uses the -mtime option, the other two become understood as well. So I will describe find’s use of the -mtime option.

As you probably know, the find command can run for minutes or hours depending on the size of the filesystem being searched. The find command makes a note of its own start time. It then looks at a file’s mtime and computes how many seconds ago the file was modified. By dividing the seconds by 86,400 (and discarding any remainder), it can calculate the file’s age in days:
Code:

0 days in seconds:       0  –   86399
1 day in seconds:    86400  –  172799
2 days in seconds:  172800  –  259159

So now that we know how many days ago a file was modified, we can use stuff like “-mtime 2” which specifies files that are 172800 to 259159 seconds older than the instant that the find command was started.

“-mtime -2” means files that are less than 2 days old, such as a file that is 0 or 1 days old.

“-mtime +2” means files that are more than 2 days old… {3, 4, 5, …}

It may seem odd, but +0 is supposed to work and would mean files more than 0 days old. It is very important to recognize that find’s concept of a “day” has nothing to do with midnight.

 

================================================================================

mohit##find /var/lib/ganglia/rrds/* ! \( -name “__SummaryInfo__” -prune  \)  -mmin +30

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Steps needed to create LUN and to make accessible by windows ISCSI initiators.

  • mohit_netapp02*> lun setup

This setup will take you through the steps needed to create LUNs
and to make them accessible by initiators. You can type ^C (Control-C)
at any time to abort the setup and no unconfirmed changes will be made
to the system.

  • Do you want to create a LUN? [y]: y
  • Multiprotocol type of LUN (solaris/windows/hpux/aix/linux/netware/vmware/windows_gpt)[linux]: windows

A LUN path must be absolute. A LUN can only reside in a volume or
qtree root. For example, to create a LUN with name “lun0” in the
qtree root /vol/vol1/q0, specify the path as “/vol/vol1/q0/lun0”.

  • Enter LUN path: /vol/test_vol/test_lun0

A LUN can be created with or without space reservations being enabled.
Space reservation guarantees that data writes to that LUN will never
fail.

  • Do you want the LUN to be space reserved? [y]: Object action: admin.util.true

Size for a LUN is specified in bytes. You can use single-character
multiplier suffixes: b(sectors), k(KB), m(MB), g(GB) or t(TB).

  • Enter LUN size: 55g

You can add a comment string to describe the contents of the LUN.
Please type a string (without quotes), or hit ENTER if you don’t
want to supply a comment.

  • Enter comment string:

The LUN will be accessible to an initiator group. You can use an
existing group name, or supply a new name to create a new initiator
group. Enter ‘?’ to see existing initiator group names.

  • Name of initiator group [windows]: Test_windows

Type of initiator group Test_windows (FCP/iSCSI) [iSCSI]: iSCSI
An iSCSI initiator group is a collection of initiator node names.Each
node name can begin with either ‘eui.’ or ‘iqn.’ and should be in the
following formats: eui.{EUI-64 address} or iqn.yyyy-mm.{reversed domain
name}:{optional string composed of alphanumeric characters, ‘-‘, ‘.’
and ‘:’}
Eg: iqn.2001-04.com.acme:storage.tape.sys1.xyz or eui.02004567A425678D
You can separate node names by commas. Enter ‘?’ to display a list of
connected initiators. Hit ENTER when you are done adding node names to
this group.

  • Enter comma separated nodenames: ?

Initiators connected on adapter ism_sw1:
iSCSI Initiator Name                  Group
iqn.1991-05.com.microsoft:appoms2   windows
iqn.1991-05.com.microsoft:colodc1.projecty.com   windows
iqn.1991-05.com.microsoft:appoff1
Enter comma separated nodenames: iqn.1991-05.com.microsoft:appoms2
Enter comma separated nodenames:
The initiator group has an associated OS type. The following are
currently supported: solaris, windows, hpux, aix, linux, netware
or vmware.

  • OS type of initiator group “Test_windows” [windows]: windows

The LUN will be accessible to all the initiators in the
initiator group. Enter ‘?’ to display LUNs already in use
by one or more initiators in group “Test_windows”.

  • LUN ID at which initiator group “Test_windows” sees “/vol/test_vol/test_lun0” [0]: 1

LUN 1 is already mapped to by initiator iqn.1991-05.com.microsoft:appoms2
in group windows
LUN ID at which initiator group “Test_windows” sees “/vol/test_vol/test_lun0” [0]: 2
LUN Path                : /vol/test_vol/test_lun0
OS Type                 : windows
Size                    : 55.0g (59057510400)
Initiator Group         : Test_windows
Initiator Group Type    : iSCSI
Initiator Group Members : iqn.1991-05.com.microsoft:appoms2
Mapped to LUN-ID        : 2

  • Do you want to accept this configuration? [y]: y
  • Do you want to create another LUN? [n]: n
  • mohit_netapp02*> lun showq

lun: unrecognized command “showq”
The following commands are available; for more information
type “lun help <command>”
aluadb              destroy             move                set
attribute           df                  offline             setup
clone               geometry            online              share
comment             help                rescan              show
config              hist                resize              snap
config_check        map                 select              stats
create              maxsize             serial              unmap
dbedit

  • mohit_netapp02*> lun show

/vol/bod_iscsi/asm1            5g (5368709120)    (r/w, online, mapped)
/vol/mohitsnap/lun0         502.0g (539019048960)  (r/w, online, mapped)
/vol/test_vol/test_lun0     55.0g (59057510400)   (r/w, online, mapped)

 

 

Maximum LUN resize limits on NetApp

Be aware there are some limits to resize the Netapp size. Due to the geometry of the LUN at the time it was created it can only be resized to a maximum of ~10 times the original size of the LUN.

One way to see this is at the command line, for the command to be available you need to run ‘priv set diag‘ and then you will have access to the ‘lun geometry‘ command. From there you can see the LUN size as well as the maximum LUN size that is available.

 

Here is a table of some of the results:

LUN Size Maximum Resize
< 50g 502g
51-100g 1004g
101-150g 1506g
151-200g 2008g
201-251g 2510g
252-301g 3012g
302-351g 3514g
352-401g 4016g

etc..

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