On 02/07/2011 03:57 PM, Ross Walker wrote: > On Mon, Feb 7, 2011 at 3:41 PM, Jason Brown > <jason.brown at millbrookprinting.com> wrote: >> On 02/07/2011 03:26 PM, Ross Walker wrote: >>> On Mon, Feb 7, 2011 at 1:56 PM, 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. >>> >>> Whatever you export, the whole disk, partition or logical volume, the >>> initiator will see as a whole disk. >>> >>> So if you mirror sdaX and sdbX and export md0 the initiator will see a >>> disk the size and contents of sdaX/sdbX. >>> >>> Just create the filesystem on the disk on the initiator and use it there. >>> >>> REMEMBER: iSCSI isn't a way for multiple initiators to share the same >>> disk (though they can using specialized clustering file systems), it >>> is a way for multiple initiators to share the same disk subsystem. >>> >>> You can't access the file system from both the target-side and >>> initiator-side at once or it will corrupt the file system. If that's >>> what you want then you want NFS or Samba and not iSCSI. >>> >> >> Well my first question would be, do you really need to partition the >> disks on the target or can you just RAID them together (ie sdb/sdc and >> not sdb1/sdc1)? Then create your md0 based off of the two drives. Once >> that is done, export the md0 in /etc/tgt/targets.conf to present to the >> clients. > > You don't need to partition the disks on the target if you want to > export the whole disks. I just don't recommend it because exporting > whole disks isn't the most economical use of the disks. The whole idea > of iSCSI is you can create one huge RAID array on the target and all > the initiators can then all benefit from it. > > If you have 13 disks, say they're 500GB SATA disks. If you create a > RAID50 out of 2 6 disk RAID5s (stripe the LVs in LVM for management > ease instead of nested mdraid devices), you would get 10x the READ > IOPS of your mirror, and the same amount or better write IOPS then the > mirror, double the write IOPS then the single RAID5 and a tad better > read IOPS then your single RAID5. Not to mention a lot more storage > potential for the two servers, or a third server, or a fourth > server... > >> Second question. This does not need to be a clustered file system as >> only one server will need access to it at a time however, if server A >> failed, could you create a new server and present it to server B and the >> new server would have access to the files or would it show as an >> unpartitioned drive? > > You can definitely allow two different hosts access to the target, > just not simultaneously (unless it's a clustered file system). The > second host can log in to the target, and have the disk at ready to > mount after the first target is offline or "fenced", just don't mount > it while it's mounted on the first target or zap! There goes your file > system! > > -Ross > _______________________________________________ > CentOS mailing list > CentOS at centos.org > http://lists.centos.org/mailman/listinfo/centos I never thought about it that way; very interesting! Thank you both for your suggestions it help out tremendously. Jason