CentOS - Feb 2008 - Re: Disk partitions and LVM limits - SUMMARY

Thank you all for the help.
I'm writing this summary message because of people requests. I haven't
tried
all of this. I just collected it and organized it.

You've got a big storage. Now what?
The short answer is: "Just connect it. It should work."

I'll play safe by saying that the following applies to <10TB storage.
Some
people reported file systems of 80TB.

Things to watch out for:
  - Make sure the driver you are using or the storage itself don't restrict 
you from making big partitions or file systems.
  - fdisk creates partitions up to 2.1TB in size. Use "parted"
instead.
  - RHEL5 supports up to 8TB ext3 file system. To create bigger then 8TB use 
option "-F" and 4K blocks.

Your options are:
  - If the storage is connected to a RAID controller you can use the 
controller to create smaller logical partitions. Then combine them with LVM.

 - If you really want to partition the drive use parted.
   While partitioning if you run into this message:
==sdb: very big device. try to use READ CAPACITY(16).
SCSI device sdb: 10248519680 512-byte hdwr sectors (5247242 MB)
sdb: Write Protect is off
==    you can just ignore it. It's informational (based on a few people 
replies).
    If you don't like parted you can still use fdisk to create a few 2TB 
partitions and then use LVM.

  - Use LVM on the raw device. Don't partition.
    This is what I did and it worked for me.
    Make sure you wipe out the MBR first:
    dd if=/dev/zero of=/dev/sdX bs=512 count=63
      (count=1 should work too but 63 won't hurt either)

    Create the pv, vg and lv:
      pvcreate /dev/sdX
      vgcreate <vg name> /dev/sdX
      lvcreate -L <size> -n <name> -v vg_name

Now you have to create the file systems. Some people recommend XFS.
If you try to create bigger then 8TB ext3 file system make sure you use
option "-F" and 4K blocks:
     mkfs -t ext3 -F -b 4096 /dev/vg00/lvol01

For more information:
  http://www.centos.org/product.html
  http://kbase.redhat.com/faq/FAQ_103_11461.shtm
  The email thread "Disk partitions and LVM limits" in CentOS, RedHat
and
     RedHat-Sysadmin mailing lists.

Thank you
Peter
> Hi,
>
> I've got a DAS DELL MD1000 with a bunch of SATA drives in RAID 5
> configuration with total space of 5.4TB. This box is attached to a
> CentOS5 system (kernel 2.6.18-53.1.6.el5).
>
> Any idea how to make this space usable?
> Is there a limit how big a partition can be? What is the work around?
> Is there a limit how big a file system ca be?
>
> I've tried to partition it but no matter how bug partition I create
> fdisk spits out these messages on the console:
> ---
> sdb: very big device. try to use READ CAPACITY(16).
> SCSI device sdb: 10248519680 512-byte hdwr sectors (5247242 MB)
> sdb: Write Protect is off
> ---
>
> I decided to not partition the drive and use LVM but the physical volume
> stopped at 2TB.
>
> So, right now I can't use LVM because of this 2TB limit and I'm not
sure
> if I partition the drive how good these partitions are because of the
> the message from fdisk.
>
> Any help or idea is highly appreciated.
>
> Thank you
> Peter

On Wednesday 13 February 2008, Peter Blajev wrote:
...
>   - fdisk creates partitions up to 2.1TB in size. Use "parted"
instead.
The difference is not fdisk vs. parted. It's MSDOS-MBR vs. GPT (different 
types of partition tables). But since fdisk doesn't support GPT you'll
have
to use parted. Note though, parted fails equally bad if you use it with 
MSDOS-MBR...

...
> Your options are:
>   - If the storage is connected to a RAID controller you can use the
> controller to create smaller logical partitions. Then combine them with
> LVM.
While this is possible it often causes performance problems (because linux now 
schedues IO independently on two devices which happen to be the same 
raid-set...).

...
>     If you don't like parted you can still use fdisk to create a few
2TB
> partitions and then use LVM.
I don't think that'll work, you can only have a MSDOS-MBR on a device
smaller
than 2T, it does not matter if your individual partitions are <2T.

/Peter K
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 189 bytes
Desc: This is a digitally signed message part.
URL:
<http://lists.centos.org/pipermail/centos/attachments/20080214/9ea01274/attachment.sig>