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I'm trying to create my own SAN out of existing hardware. I have four identical NAS devices. Each one has four 1 TB drives that they do RAID-5 across. On each NAS I have created a 1 TB iSCSI share. I have another linux server that connects to each iSCSI target. On this server I have created a RAID 10 array of these iSCSI devices. I then plan to share this array out via NFS. With this setup I could survive several hard drive failures and even lose a whole NAS. But I also want to have a second NFS server as well. It sounds like my second server should be able to connect to the iSCSI targets without a problem but I'm not sure what will happen when I try to create the RAID 10 array.

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is there a question here? No one is sure what will happen when you try to create the RAID 10 array, because this is YOUR custom setup... –  August Sep 16 '11 at 16:32
    
I guess my question is if it's possible to duplicate my server managing the RAID array while using the same iSCSI targets? Since the array is being built on raw devices I can't stick another layer in there like GFS. –  J.R. Sep 16 '11 at 16:51
    
I think you are going to end up with latency and performance problems in this setup. You are using a NAS to create an iSCSI LUN - most prosumer level NASes (heck, even professional ones) don't have great iSCSI performance due to the way they have to implement a LUN in their filesystem, as well as their particular iSCSI implementation. Then you go via iSCSI over Ethernet to a central server, and then serve it out over NFS.... it just seems like a recipe for poor performance. Why not just get a SAS enclosure for this centralized server and put all your 1TB drives in it, then run that? –  Jeremy Oct 2 '11 at 15:17
    
My goal was to add redundancy and performance to our setup without spending more money. I did several I/O tests along the way and there was no difference between NFS and iSCSI going directly to the NAS. I did see a performance boost when I added RAID-10. I also addressed my question here by using ucarp to share the same IP across the two servers. As soon as one goes down the other one takes over the RAID-10 and NFS export. It's not the prettiest setup but it's an improvement from before and we didn't have to purchase any new equipment or software. –  J.R. Oct 2 '11 at 17:21
    
@JR - But did you test latency? –  Jeremy Oct 4 '11 at 16:52
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While this is an interesting approach, I believe you are correct in realizing that the software RAID-10 won't work when you try to extend it to another server. Instead, I think you'll need something like DRDB or GlusterFS to achieve your goals (or possibly both, and/or a clustering filesystem like OCFS2 or GFS).

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