School me on iSCSI

Discussion in 'OT Technology' started by deusexaethera, Oct 7, 2008.

  1. deusexaethera

    deusexaethera OT Supporter

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    I've read a few things online about iSCSI, I know it's a way to build a SAN out of what would otherwise be normal servers and networking hardware, but I'm missing the part that explains why I would want to do this. Can I boot from iSCSI? Is it faster than a regular network share or mapped drive? Does it offer some useful abstraction? Or is it something else?
     
  2. Harry Caray

    Harry Caray Fine purveyor of x.264, h.264 & TS HD-Video !!! HD

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    It's called Wikipedia... and google... use it
     
  3. deusexaethera

    deusexaethera OT Supporter

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    I already did. Still not understanding why I would want to use iSCSI.
     
  4. trouphaz

    trouphaz New Member

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    there are certain things that do not work well (or work at all) with a network share. in those cases you need to actually have a disk available to the system. one example was some FTP service for Windows. i think it might actually be IIS. one of the guys i worked with couldn't configure a directory to be the ftp location if it was a network share.

    i also think that the overhead of CIFS or even NFS is much worse than that of iSCSI. so you can theoretically get better performance out of an iSCSI device than a network share.

    next, in a highly available environment, to use a network share complicates the environment. you have the storage, the file server and the app server which is a client to the file server that all need to be redundant. if you aren't using iSCSI, the file server either needs to be fiber attached to the SAN or direct attached to the storage. then, that file server needs to be in a clustered environment. and then the app layer also needs to be clustered for redundancy. or, you can bypass the file server layer and just have iSCSI storage with network redundancy connected to a application cluster.
     
  5. deusexaethera

    deusexaethera OT Supporter

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    So, if I have two file servers in separate offices, and they're synched nightly using DFS Replication, could I set up something where machines automatically try to connect to the local server and, failing that, connect to the remote server, without bothering the user about it?

    What if some of those machines are laptops and they sometimes don't have access to either server? Would that break the setup?
     
  6. crontab

    crontab (uid = 0)

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    The upcoming pNFS should eliminate the overhead it currently has over block I/O. Oracle has something similar embedded into their kernel/app and according to them, it provides good performance, good for them, when users want to run a db off a NFS share, some high performance NAS. Our HPCC's do something similar as well, the compute nodes all talks to the storage nodes via NFS and paths are fanned out to the storage nodes.

    We are not going to be buying any more FC going forward and will slowly be migrating to iSCSI. We will segregate this network infrastructure from all other IP traffic. Just a group of dedicated of switches for this, similar to our fiber switch infrastructure. Many many adopters plop an IPSAN into their existing network and tag that traffic. I don't see how this is a good idea, other than it being the cheapest. This will work fine for business with low budgets and low performance needs.

    Note, FC will not be going any further with fiber, they are stopping at 8x, no 16x, 32x, 64x, etc. They are jumping on the Ethernet bandwagon with FCoE, which is pretty much FC wrapped around iSCSI, even MORE overhead.

    Did you attend the Storage Conference in NYC a couple weeks ago? There were a lot of sessions of FC vs. ISCSI.
     
  7. trouphaz

    trouphaz New Member

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    i'm not really sure what your talking about or what it has to do with iSCSI. iSCSI is a replacement for either connecting your host directly to your storage array or even connecting over a fiber switch. the host sees the iSCSI lun the same way as it would any other disk. so, you can partition it, format it, use it for a cluster device, etc.
     
  8. deusexaethera

    deusexaethera OT Supporter

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    The idea is I want to make two mirrored fileservers in separate offices available as a high-availability iSCSI volume on each of the workstations in my office. I know those workstations used to be configured to connect to an FC SAN using FC workstation cards back when all that equipment was owned by a company we bought, so it should be possible to do the same without the specialized hardware. It's the mirroring and the automatic failover that I'm not sure how to deal with.
     
  9. JayC71

    JayC71 Guest

    http://www.openfiler.com/products

    It's useful for low I/O things like labs and testing. iSCSI in VMware is becoming more and more useful as VMware supports more features over it.
     
  10. trouphaz

    trouphaz New Member

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    one of us isn't understanding the other. i don't think you want iSCSI for what you are doing. you can present an iSCSI lun to your workstation, but there will be no data on it. iSCSI gives you block level access to disk from a host who can partition it and format it the same as an internal disk.

    iSCSI is equal to fiber attached SAN in functionality. it is not a direct replacement for a CIFS share. iSCSI does not offer the same functionality as CIFS. yes, both offer the ability to access storage across the network, but in completely different ways.


    so, if you have a central location that has a ton of disk that you want to make available to hosts who do not have fiber connectivity, you can use iSCSI to give them disk.
    if you have a file server (which you do) that you want to make accessible to multiple workstations, then you want CIFS. and just to confuse you, you can assign iSCSI storage to the file server that he can create his filesystems on and share out through CIFS.
     

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