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Old 02-23-2010, 02:38 PM
Khusro Jaleel
 
Default creating partitions on a 2.7TB drive

Hello, sorry for the long email, it's a little hard to explain this issue. The gist of it is that the Ubuntu version of parted allowed me to do something which perhaps should not be allowed i.e. creating partitions on a 2.7TB drive when the partition table is not *gpt* but *msdos*.

I am trying to configure 2 identical servers, both are Dell Poweredge 2970 machines with 6 disks in them configured as a RAID 5 with one hotspare, and both give me 2.726TB of space after the RAID 5 is configured. There are slight differences between the BIOS versions and Firmware versions of the LSI disk controller, etc but I'm not sure that matters in this case.

Now, I setup server "A" a few months ago and for some reason that I don't remember now I resorted to using a Ubuntu 64-bit LiveCD to create the partitions. Since the disk is larger than 2TB, I had to use 'parted' to create the partitions. So I happily created the partitions I wanted which are below:

/ 50 GB
/var 20 GB
/data the remainder (a large partition)

Now, after a few months I forgot all about the Ubuntu LiveCD and tried to setup server "B" using the CentOS 5.3 x86_64 CD. However the installer immediately complained that "this disk in using a GPT partition table and this computer cannot boot using GPT" and it keeps saying this no matter what I do. I've tried creating a separate /boot partition, using LVMs for everything, etc but nothing works, even "dd" did not give me much luck, although perhaps I should try deleting the "end" of the disk rather than the beginning?

I have now noticed that when press Ctrl-Alt-F2 on server "B" during the CentOS install and attempt to use 'parted' it says that the "label" type is "gpt". It allows me to create new partitions, etc but it's no help because the installer keeps complaining that the machine will not boot with a GPT partition table. So I need to really use a "msdos" partition type to boot this machine successfully, but the CentOS version of parted will not allow me to do that.

The additional mystery is that if I check server "A" which I partitioned a few months ago using Ubuntu, the "label" type is "msdos"!! How is that possible? In addition if I use the CentOS CD and try to use parted on server "A" now, it gives the following error:

---------------------------
# parted
GNU Parted 1.8.1
Using /dev/sda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) p
Error: msdos labels do not support devices that have more than 4294967295 sectors.
---------------------------

BUT if I reboot this same server (server A) again using the Ubuntu LiveCD parted works just fine! It prints the label type as "msdos", and it prints the above partition table correctly and gives me the right size for it and everything.

So what is going on here? Is the Ubuntu parted somehow buggy and allowing me to do something dangerous that I will regret later, or can I just ignore the label setting in parted and continue to setup Server "B" the same as "A" and hope for the best?

I would appreciate any insights.

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Old 02-23-2010, 02:45 PM
Eero Volotinen
 
Default creating partitions on a 2.7TB drive

2010/2/23 Khusro Jaleel <mailing-lists@kerneljack.com>:
> Hello, sorry for the long email, it's a little hard to explain this issue. The gist of it is that the Ubuntu version of parted allowed me to do something which perhaps should not be allowed i.e. creating partitions on a 2.7TB drive when the partition table is not *gpt* but *msdos*.
>
> I am trying to configure 2 identical servers, both are Dell Poweredge 2970 machines with 6 disks in them configured as a RAID 5 with one hotspare, and both give me 2.726TB of space after the RAID 5 is configured. There are slight differences between the BIOS versions and Firmware versions of the LSI disk controller, etc but I'm not sure that matters in this case.
>
> Now, I setup server "A" a few months ago and for some reason that I don't remember now I resorted to using a Ubuntu 64-bit LiveCD to create the partitions. Since the disk is larger than 2TB, I had to use 'parted' to create the partitions. So I happily created the partitions I wanted which are below:

I think it is not possible to create partitions lager than 1.7TB
without gpt partition table.

Of course you can create small boot partition and some lvm partitions
and combine them to one big lvm volume or use another drive for
booting and use gpt partition table for big disk..

--
Eero
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Old 02-23-2010, 02:47 PM
Joshua Baker-LePain
 
Default creating partitions on a 2.7TB drive

On Tue, 23 Feb 2010 at 3:38pm, Khusro Jaleel wrote

> Now, after a few months I forgot all about the Ubuntu LiveCD and tried
> to setup server "B" using the CentOS 5.3 x86_64 CD. However the
> installer immediately complained that "this disk in using a GPT
> partition table and this computer cannot boot using GPT" and it keeps
> saying this no matter what I do. I've tried creating a separate /boot
> partition, using LVMs for everything, etc but nothing works, even "dd"
> did not give me much luck, although perhaps I should try deleting the
> "end" of the disk rather than the beginning?

There are 2 facts at play here:

1) Any device larger than 2TB must use a GPT disklabel.

2) You cannot boot from a device with a GPT disklabel.

None of the tricks you mention above will work. What you need to do is
use the RAID card BIOS to divide the array into multiple devices. Most
decent RAID cards will either "auto-carve" arrays into <2TB chunks or let
you create a small "boot-drive". The latter is preferable, IMO. If your
RAID card doesn't offer such an option, then you'll need to either remove
some disks from the array to use as boot drives or add more drives to the
system.

> The additional mystery is that if I check server "A" which I partitioned
> a few months ago using Ubuntu, the "label" type is "msdos"!! How is that
> possible? In addition if I use the CentOS CD and try to use parted on
> server "A" now, it gives the following error:

Weird things happen when trying to boot from GPT labeled devices,
including all sorts of data-loss scenarios.

--
Joshua Baker-LePain
QB3 Shared Cluster Sysadmin
UCSF
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Old 02-23-2010, 02:48 PM
Tim Shubitz
 
Default creating partitions on a 2.7TB drive

On Feb 23, 2010, at 9:38 AM, Khusro Jaleel wrote:

> I am trying to configure 2 identical servers, both are Dell Poweredge 2970 machines with 6 disks in them configured as a RAID 5 with one hotspare, and both give me 2.726TB of space after the RAID 5 is configured. There are slight differences between the BIOS versions and Firmware versions of the LSI disk controller, etc but I'm not sure that matters in this case.

I had this exact issue with the exact hardware and setup you describe above.


> So what is going on here?

I believe that the issue is with the Anaconda.


> Is the Ubuntu parted somehow buggy and allowing me to do something dangerous that I will regret later, or can I just ignore the label setting in parted and continue to setup Server "B" the same as "A" and hope for the best?
>
> I would appreciate any insights.

Here is what I ended up doing...


In the hardware RAID controller I setup a "virtual drive" of 50GB and another virtual drive made from the remaining space.

Here is a nice ASCII description of the RAID setup.

0 - 750GB SATA --- Global Hot spare

1 - 750GB SATA ----
2 - 750GB SATA -----
3 - 750GB SATA ------> RAID 5 == ~2.7 TB
4 - 750GB SATA -----/
5 - 750GB SATA ----/

VD = Virtual Disk

VD 0 (sda) - 50GB (boot volume [/boot, /, /home, /tmp, etc.])
VD 1 (sdb) - <remaining space> ("data" storage, /var)

After saving those changes within the RAID controller I then booted the CentOS 5.4 x86_64 installer and installed away.

Hope that helps.


- tim


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Old 02-23-2010, 03:03 PM
Robert Heller
 
Default creating partitions on a 2.7TB drive

At Tue, 23 Feb 2010 17:45:34 +0200 CentOS mailing list <centos@centos.org> wrote:

>
> 2010/2/23 Khusro Jaleel <mailing-lists@kerneljack.com>:
> > Hello, sorry for the long email, it's a little hard to explain this issue. The gist of it is that the Ubuntu version of parted allowed me to do something which perhaps should not be allowed i.e. creating partitions on a 2.7TB drive when the partition table is not *gpt* but *msdos*.
> >
> > I am trying to configure 2 identical servers, both are Dell Poweredge 2970 machines with 6 disks in them configured as a RAID 5 with one hotspare, and both give me 2.726TB of space after the RAID 5 is configured. There are slight differences between the BIOS versions and Firmware versions of the LSI disk controller, etc but I'm not sure that matters in this case.
> >
> > Now, I setup server "A" a few months ago and for some reason that I don't remember now I resorted to using a Ubuntu 64-bit LiveCD to create the partitions. Since the disk is larger than 2TB, I had to use 'parted' to create the partitions. So I happily created the partitions I wanted which are below:
>
> I think it is not possible to create partitions lager than 1.7TB
> without gpt partition table.
>
> Of course you can create small boot partition and some lvm partitions
> and combine them to one big lvm volume or use another drive for
> booting and use gpt partition table for big disk..

Random odd thought. It sounds like you are using a hardware RAID
controller (LSI)? I know that the old Mylex RAID controllers would
allow you to create multiple *logical* disks on top of a RAID set. Can
you do this with the LSI RAID controller? If so, what I would do is
create two logical disks, one 'small' (say 20gig or so) and one large
(whatever is left). Then, install CentOS on the 20gig logical disk,
using a MS-DOS partition table as CentOS wants to do (I'd do four
partitions: /boot swap / and /home). *Don't* even try to partition the
big disk. Just make it an LVM PV and then create a VG with this
physical volume. Carve out logical volumes as needed.

>
> --
> Eero
> _______________________________________________
> CentOS mailing list
> CentOS@centos.org
> http://lists.centos.org/mailman/listinfo/centos
>
>

--
Robert Heller -- 978-544-6933
Deepwoods Software -- Download the Model Railroad System
http://www.deepsoft.com/ -- Binaries for Linux and MS-Windows
heller@deepsoft.com -- http://www.deepsoft.com/ModelRailroadSystem/

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Old 02-23-2010, 03:11 PM
Khusro Jaleel
 
Default creating partitions on a 2.7TB drive

Thanks for your replies, just to clear things up, here is what I am seeing.

If I reboot server "A" with the Ubuntu LiveCD, I get:
----------------------------------------
# parted /dev/sda p

Model: DELL PERC 5/i (scsi)
Disk /dev/sda: 2998GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number Start End Size Type File system Flags
1 32.3kB 53.7GB 53.7GB primary ext3
2 53.7GB 62.3GB 8595MB primary linux-swap
3 62.3GB 83.8GB 21.5GB primary ext3
4 83.8GB 2199GB 2115GB primary xfs

# fdisk -l

Disk /dev/sda: 2998.4 GB, 2998424043520 bytes
255 heads, 63 sectors/track, 364537 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x852b68e5

Device Boot Start End Blocks Id System
/dev/sda1 1 6528 52436128+ 83 Linux
/dev/sda2 6529 7573 8393962+ 82 Linux swap / Solaris
/dev/sda3 7574 10185 20980890 83 Linux
/dev/sda4 10186 267349 2065669830 83 Linux
----------------------------------------

Now when I try this with CentOS, I get:
----------------------------------------
Error: msdos labels do not support devices that have more than 4294967295 sectors.
-----------------------------------------

straight away. I understand what you guys are saying about GPT and not being able to boot off it, etc but how did I end up in this situation? And is this dangerous?

I am thinking that if this is possible, why not try and setup the second server the same way? But it just feels wrong that Ubuntu allows this and if CentOS does not, there must be a good reason.


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Old 02-23-2010, 04:57 PM
Joshua Baker-LePain
 
Default creating partitions on a 2.7TB drive

On Tue, 23 Feb 2010 at 4:11pm, Khusro Jaleel wrote

> straight away. I understand what you guys are saying about GPT and not
> being able to boot off it, etc but how did I end up in this situation?

There's an old saying that Unix gives you enough rope to hang yourself
with...

> And is this dangerous?

Yes. Absolutely yes. One day you'll reboot and your partition table (and
all your data) will be gone and unrecoverable. Trust me.

> I am thinking that if this is possible, why not try and setup the second
> server the same way? But it just feels wrong that Ubuntu allows this and
> if CentOS does not, there must be a good reason.

And that reason is that it *will* die horribly and eat your data. Set up
the small logical drive in the RAID BIOS as another poster detailed so
nicely. Now. Before now.

--
Joshua Baker-LePain
QB3 Shared Cluster Sysadmin
UCSF
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