How to know exactly which physical partion contains data? Post: 302928469

Sponsored Content

Operating Systems AIX How to know exactly which physical partion contains data? Post 302928469 by bakunin on Friday 12th of December 2014 02:49:12 AM

12-12-2014

Registered User

Quote:

Originally Posted by bobochacha29

As you said above, data is written randomly to the disk and these lp/pp listed above have no relationship with the filesytem space used/free.

Yes and no. data is not written entirely randomly. There is a system behind it, but it is complex. You seem to have meant that a filesystem which is, say, 50% full and consists of LPs1-10 will have the LPs1-5 written full and LPs6-10 empty. This is (typically) not the case. Typically (depending on what the content of your filesystem is - many small files or a few large files or some mix of both, how often the data on disk changes and some other specifics) your filesystems space will be scattered and every LP will be nearly 50% full and nearly 50% empty.

Furthermore, if a FS resides on a LV which consists of 10 LPs these are ordered 1-10. But that does not have to mean that LP3 is "behind" LP2 on disk. It could well be that LP1 is at PP200, LP2 is at PP100 and LP3 is at PP150 (with maybe other LVs taking the place in between). For the filesystem the space would still appear to be linear, first the space coming from LP1, then from LP2, etc.. The FS will be unaware of the fact that to go from LP1 to LP2 this means to skip many PPs on disk.

Quote:

Originally Posted by bobochacha29

The data may reside anywhere on these 40 pps and there's no way to know that.

Yes, it is possible to find out, but no, there is no 1:1-relation you could use. Say, you have some file. If you want to know where the first byte of the file "/path/to/some/file" is located on the disk you can find out on which place the first (filesystem) block of your file is. Then, using LV methods, find out on which LP this part of the filesystem really is. After this, you use the LP-PP-relation you already have posted to find out which PP is used to represent this LP and finally you can use VG-methods to locate the PP on some specific place on some specific disk and use low-level methods ("dd" and the like) to really find that part of the file you started with.

But, having found that out for byte X doesn't mean that you could read the next byte on disk and expect to find the content of byte X+1 in the file. This may be so or not, but to know that you will need to exercise the whole procedure again.

I hope this helps.

bakunin

This User Gave Thanks to bakunin For This Post:

bakunin

View Public Profile for bakunin

Find all posts by bakunin

9 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

Partion size

hi, just need to know the disk size and the partition size on machine.pls let me know how to do that.is their a way i can get to know the size of directory.like /,/var...etc. thanx

2. UNIX for Dummies Questions & Answers

physical volume and physical disk.

Hello, I need explanations about physical disks and physical volumes. What is the difference between these 2 things? In fact, i am trying to understand what the AIX lspv2command does. Thank you in advance.

3. Linux

Doing stuff to files on a NTFS partion from linux

I have a 50GB section of my hard drive on which I've kept all my music, movies and more back from when I had Windows. When I'm in linux it says that the NTFS section is a read only section. Is it possible to copy, rename, add, move or delete any files off of this section? I'm trying to get rid...

4. UNIX for Dummies Questions & Answers

Partion Magic problems.

Hiya people, A great big "HI" to everybody. I'm new to the Forum and now to my problem(s). I am about to partition my only 80GB HD and using the Partition Magic 8 software it looks fairly simple although here is my problem :- 1. Do I change the new partition to primary or logical? 2. Do I...

5. UNIX for Dummies Questions & Answers

Physical volume- no free physical partitions

I was in smit, checking on disc space, etc. and it appears that one of our physical volumes that is part of a large volume group, has no free physical partitions. The server is running AIX 5.1. What would be the advisable step to take in this instance?

6. Solaris

How to create on partion from 2 disks?

Hi everyone :b: I'm glade to join this forum and I have one question I installed latest Solaris 10 release on SF V480 with 2 73 GB disks 8 GB RAM 4 CPU's My configuration is 10GB for root, 8GB for Swap and 12GB for var. I mirrored root, so disk 1 has 40GB free of space and disk 2 has...

7. Shell Programming and Scripting

Auto XP partion restore

At my computer shop where I work, we got alot of used PC's from some place. It's my job to refurbish them for resale. Each computer comes with XP pro. So the boss man asks me if there is a way to put a XP restore option. I say yes if I install Linux on a small partion and use partimage to make a...

8. Linux

Centos 5 install. Partion order

I can't control the partion order during install. For example i need. hda5 /var 1GB hda6 /opt 2GB I created them in such order but OS adjust them to hda5 /opt 2GB hda6 /var 1GB It is frustrating during install, I pretty sure I can order the partion as i like...

9. AIX

Maximum Limit of HMC to handle Physical Power Virtualization Physical Machine

Hello All, Can anybody please tell me what is the maximum limit of Physical IBM Power Machine which can be handled by single HMC at a single point of time? Thanks, Jenish

LEARN ABOUT OSX

quotacheck

QUOTACHECK(8)						    BSD System Manager's Manual 					     QUOTACHECK(8)

NAME

     quotacheck -- filesystem quota consistency checker

SYNOPSIS

     quotacheck [-g] [-u] [-v] filesystem ...
     quotacheck [-g] [-u] [-v] -a

DESCRIPTION

     Quotacheck examines each filesystem, builds a table of current disk usage, and compares this table against that recorded in the disk quota
     file for the filesystem.  If any inconsistencies are detected, both the quota file and the current system copy of the incorrect quotas are
     updated (the latter only occurs if an active filesystem is checked).  By default both user and group quotas are checked.

     Available options:

     -a      If the -a flag is supplied in place of any filesystem names, quotacheck will check all the read-write filesystems with an existing
	     mount option file at its root.  The mount option file specifies the types of quotas that are to be checked.

     -g      Only group quotas are checked. The mount option file, .quota.ops.group, must exist at the root of the filesystem.

     -u      Only user quotas are checked.  The mount option file, .quota.ops.user, must exist at the root of the filesystem.

     -v      quotacheck reports discrepancies between the calculated and recorded disk quotas.

     Specifying both -g and -u is equivalent to the default.  Parallel passes are run on the filesystems required, in an identical fashion to
     fsck(8).

     Normally quotacheck operates silently.

     Quotacheck expects each filesystem being checked to have quota data files named .quota.user and/or .quota.group located at the filesystem
     root.  If a binary data file is not present, quotacheck will create it.  The default filename and root location cannot be overridden.

     Quotacheck is normally run at fsck time.

     Quotacheck accesses the raw device in calculating the actual disk usage for each user.  Thus, the filesystems checked should be quiescent
     while quotacheck is running.

FILES

     Each of the following quota files is located at the root of the mounted filesystem.  The mount option files are empty files whose existence
     indicates that quotas are to be enabled for that filesystem. The binary data files will be created by quotacheck, if they don't already
     exist.

     .quota.user       data file containing user quotas
     .quota.group      data file containing group quotas
     .quota.ops.user   mount option file used to enable user quotas
     .quota.ops.group  mount option file used to enable group quotas

SEE ALSO

     quota(1), quotactl(2), edquota(8), fsck(8), quotaon(8), repquota(8)

HISTORY

     The quotacheck command appeared in 4.2BSD.

4.2 Berkeley Distribution					 October 17, 2002					 4.2 Berkeley Distribution