[CentOS] iSCSI disk preperation

Mon Feb 7 20:32:41 UTC 2011
Jason Brown <jason.brown at millbrookprinting.com>

On 02/07/2011 02:36 PM, Dr. Ed Morbius wrote:
> on 13:56 Mon 07 Feb, Jason Brown (jason.brown at millbrookprinting.com) wrote:
>> I am currently going through the process of installing/configuring an
>> iSCSI target and cannot find a good write up on how to prepare the disks
>> on the server.  I would like to mirror the two disks and present them to
>> the client.  Mirroring isn't the question, its how I go about it is the
>> problem.  When I partitioned the two drives and mirrored them together,
>> then presented them to the client, it showed to the client as a disk out
>> no partion on it.  Should I partition the drive again and then lay the
>> file system down on top of that?  Or should I delete the partitions on
>> the target server and just have sda and sdb mirrored, then when the
>> client attaches the disk, then partion it (/dev/sdc1) and write the file
>> system.
> What are you using for your iSCSI target (storage array)?
> Generally, RAID management of the storage is managed on the target side.
> You'd use the target's native abilities to create/manage RAID arrays to
> configure one or more physical disks as desired.  If you're using a
> dedicated vendor product, it should offer these capabilities through
> some interface or another.
> Presentation of the iSCSI device is as a block storage device to the
> initiator (host mounting the array).  That's going to be an
> unpartitioned device.  You can either further partition this device or
> use it as raw storage.  If you're partitioning it, and using multipath,
> you'll have to muck with kpartx to make multipath aware of the
> partitions.
> We've elected to skip this locally and create a filesystem on the iSCSI
> device directly.
> Creating and mounting filesystems are both generally managed on the
> initiator.
> Truth is, there's a lot of flexibility with iSCSI, but not a lot of
> guidance as to best practices that I could find.  Vendor docs have
> tended to be very poor.  Above is my recommendation, and should
> generally work.  Alternate configurations are almost certainly possible,
> and may be preferable.

I realize now that I left out quite a bit of information from my OP.

The iSCSI target is going to be used to storage, which has 13 disks to
be presented and would like these split up between two LUNs.  One which
will be mirrored and the second LUN which will be RAID 5; each LUN going
to different servers.  The iSCSI target will use CentOS 5.5 with
software RAID and the initiators will be CentOS 5.5 as well.

Here are the steps that I tried when I set this up:
1) Created partitions on sdh and sdi
2) RAID'ed sdh1 and sdi1
3) Mounted the disk on the client which then became sdc (this started
the confusion as to why it wasn't sdc1)
4) Partitioned sdc to sdc1
5) Created an LV sdc1
6) Mounted everything fine and added the LV to fstab
7) Rebooted the server and SELinux freaked out which put the system into
rescue mode
8) Removed the storage from fstab, did an '/.autorelabel' and rebooted
9) When the system came back up the lvm was not in /dev however I could
see it in lvdisplay

Since then I've tried looking for a best practice guide as to how do
properly configure the disks but have not been able to find anything.