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how to tell if a server boots from SAN

Posted on 2011-03-10
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Last Modified: 2012-05-11
I have a Fedora server that I believe boots from a SAN. However how can I tell for sure if this is the case from the server itself. how would I go about doing this? here is some information about the drives.






fdisk -l

Disk /dev/sda: 250.0 GB, 250000000000 bytes
255 heads, 63 sectors/track, 30394 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      104391   83  Linux
/dev/sda2              14       30394   244035382+  8e  Linux LVM






mount
/dev/mapper/VolGroup00-LogVol00 on / type ext3 (rw)




lvdisplay
  --- Logical volume ---
  LV Name                /dev/VolGroup00/LogVol00
  VG Name                VolGroup00
  LV UUID                fs7sUC-4KNe-Zz54-YozX-GDux-PQpC-vBhYKY
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                225.00 GB
  Current LE             7200
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0

  --- Logical volume ---
  LV Name                /dev/VolGroup00/LogVol01
  VG Name                VolGroup00
  LV UUID                lZ4XP1-ZdON-vZCW-lxxv-pjyK-Tinq-mbM1Bv
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                7.69 GB
  Current LE             246
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1





pvdisplay
  --- Physical volume ---
  PV Name               /dev/sda2
  VG Name               VolGroup00
  PV Size               232.73 GB / not usable 11.80 MB
  Allocatable           yes
  PE Size (KByte)       32768
  Total PE              7447
  Free PE               1
  Allocated PE          7446
  PV UUID               jeXX7v-k7Ll-DoP7-ZJ6M-S0Ad-z41X-ukgShr
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Question by:ryan80
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12 Comments
 
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Expert Comment

by:farzanj
ID: 35100798
Do
df -hT /boot

I am interested to know where the /boot is located.  That is where it boots from, at least the second stage of its booting.  The first stage always takes place from the first 570 or sectors of the local drive
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Expert Comment

by:farzanj
ID: 35100823
From what I can see, I don't see any SAN.

All what I see is logical volume.  It is probably booting from /dev/sda2 which contains your logical volume.
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Expert Comment

by:farzanj
ID: 35100867
If you look carefully, your physical volume is based entirely on your /dev/sda2, which is your SCSI drive, and is local to your computer. Your volume group is based entirely on this physical volume, nothing else.
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LVL 12

Author Comment

by:ryan80
ID: 35100967
df -hT /boot
Filesystem    Type    Size  Used Avail Use% Mounted on
/dev/sda1     ext3     99M   15M   80M  16% /boot
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LVL 12

Author Comment

by:ryan80
ID: 35101039
There is a system in place here, Cobbler, that is used for making PXE boot configs.

I see the IP address of this server in the Cobbler system, but there is no mac address configured which I thought would be neccesary for PXE boot to work.

Now if a system uses PXE boot, does that mean that the OS will be located on the network? or can it be used just to install an OS onto the local drive(s)?
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Expert Comment

by:farzanj
ID: 35101235
So your system is getting booted from /dev/sda1, which is local to your system and is the correct way to do it.  We don't recommend putting /boot even on the LVM.  It is a bad practice but still very senior admins do it.
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Expert Comment

by:farzanj
ID: 35101259
Yes, that is the idea behind the PXE boot.  You can install your systems over the network.  So there are numerous technologies that run behind the scene.  What kind of OS is it?

For stage1 boot phase, tftp is used using PXE, and for stage 2 boot, ftp, nfs, http may be used.
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Author Comment

by:ryan80
ID: 35103178
It is Fedora 9
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Expert Comment

by:farzanj
ID: 35104337
For Fedora, I believe you should be using PXE and then Kickstart mechanism.  This part is different for all OSs.  Redhat family goes by kickstart which is very powerful mechanism for doing a custom install.

This should answer all your questions.  Anything else?
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LVL 12

Author Comment

by:ryan80
ID: 35104913
Sorry I thought I had posted another post. Last one.

Is an sda always local? How do you actually tell that something is a network drive (whether nfs, fixer channel, iscsi)?
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LVL 31

Accepted Solution

by:
farzanj earned 2000 total points
ID: 35108647
It depends upon your hardware.

If it is a SAN device, its name would be a little different.  It would never be /dev/sdaX or /dev/sdbX etc.

For example

/dev/cciss/c0d0: (Smart Array P800) RAID 0 Volume 0 status: OK.
/dev/cciss/c0d0: (Smart Array P800) RAID 0 Volume 1 status: OK.
/dev/cciss/c0d0: (Smart Array P800) RAID 1 Volume 2 status: OK.
/dev/cciss/c0d0: (Smart Array P800) RAID 5 Volume 4 status: OK.
/dev/cciss/c0d0: (Smart Array P800) RAID 5 Volume 5 status: OK

I hope that makes sense.  You can see at your work, what device paths are the SANs using.  What kind of SAN do you have?  If you find it is different than what I showed, please post it here too


Last, booting NEVER happens at SAN.  Your system is configured right.  Ideally it should be a primary partition on the local drive and this is exactly what your system has.  Stage 1 booting always happens at the MBR (master boot record) of your drive.  Boot partition should ideally be separate from root partition as you have.

If I have missed anything else, please let me know.
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Author Closing Comment

by:ryan80
ID: 35112535
Thanks, that is what I thought.

the SAN is using fibre channel and there is a multi path driver that is installed to reach it. The device path shows as

/dev/mapper/mpath0p1

Thanks for your patience with walking me through this. i really appreciate it and have a much better grasp on this now.
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