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Removing disks from a SAN

Discussion in 'Hardware' started by simongrahamuk, Dec 14, 2009.

  1. simongrahamuk
    Honorary Member

    simongrahamuk Hmmmmmmm?

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    My experience with SANs is virtually non existant (I usually deal with NAS), so whilst I'll be googling for a solution to this I though I'd ask the experts.

    Is it possible to remove a group of disks from a SAN without affecting the data on the other disks, and leave them out of the SAN completely?

    Ok, here's the scenario - I have a setup that has three main servers, all connected to the SAN (its DELL iSCSI BTW). each server has logical disk space allocated on the SAN and as far as I know uses its own set of disks. So server1 for example uses the first 7 disks, server2 the second 7, etc.

    Now I want to permanently remove the disks from the SAN that are allocated to server2, and by permanently I mean physically. What I also need to be able to do is to do this without affecting the setup of the other servers connecting to the SAN. Is this possible?

    Incidently if anyone was wondering I'm looking to re use the disks that are removed from the SAN locally in the servers, as the whole way that the SAN is setup is far more complicated than it needs to be.
     
  2. danielno8

    danielno8 Gigabyte Poster

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    I am by no means a SAN expert, but the the SAN i used definately wasn't configured like that.

    We had two SAN storage modules, with 12 drives each. They 2 modules were mirrored, and each module was configured with a flavour of RAID. Not sure which. But basically when creating volumes there was no option to create the volumes on specific drives.
     
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  3. simongrahamuk
    Honorary Member

    simongrahamuk Hmmmmmmm?

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    You may well be right.

    I can only go on the information I have been given, and this is the way that I've been told it is setup. Like I said, the whole reason for looking into this is beacuse it's setup is more complicated than it needs to be.
     
  4. onoski

    onoski Terabyte Poster

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    SAN is a complicated system as that you're very correct about. However, depending on the brand i.e. Dell or HP etc. Ours for instance is HP and the unit that encompasses the SAN build is the enclosure that sits on a rack.

    Hence, you can have several enclosures each with its hard drive and and mezzine card. The mezzine card is the network adapter card. I am by no means a SAN expert but from our current setup you can't just take our a hard disk as it's part and parcel of the SAN build attached to some sort of SCSI interface.

    Best wishes and lets know how you get on:)
     
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  5. simongrahamuk
    Honorary Member

    simongrahamuk Hmmmmmmm?

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    As far as I'm aware the SAN in question has two enclosures, a DELL MD3000, and a DELL MD1000. My understanding is that the MD3000 has two controllers on it, and the MD1000 is simply configured as a slave device?

    I'm not sure where the disks in the MD1000 are allocated at present, but (I've been told) that the ones in the MD3000 are set up as per my original post.

    I'n an ideal world I'd like to completely flatten the SAN setup an re do it the way that I wan't it, but unfortunately that is not an option at the moment.
     
  6. Theprof

    Theprof Petabyte Poster Forum Leader

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    I am no expert either, but I am assuming it has some sort of raid on the SAN for redundancy? Also keep in mind any disk you remove or add, the RAID has to be rebuilt. We have an HP SAN and through the management console, we do have the options of removing a disk. In theory you should be able to do that as long as you have enough space for data after you remove the disks.
     
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  7. Phoenix
    Honorary Member

    Phoenix 53656e696f7220 4d6f64

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    ok so heres how it normally goes
    and i'd totally advise not throwing those disks in locally without first working out your san, its more complicated because its not understood yet!


    so, the MDS3000 is the controller shelf, probably with disks too, and the MDS1000 is the add on shelf, just disks, connected to the parent shelf, usually via SAS cables (or SCSI if its old)

    the SAN carves the disks into RAID GROUPS, this is almost always the case, even with funky netapp stuff ;)
    raidgroups are sets of disks with a raid stripe across them, this is often not all the drives in a SAN due to the failure chances increasing

    on top of RAID groups, you create LUNS, luns are what are presented to servers as disks (drives)
    you can remove the LUNS and the server no longer sees drives show up from the SAN
    but if you have LUNS for more than one server on the same raid group and start removing disks your screwed

    it sounds like your saying one server has a raid group dedicated to it, with luns on top of it, and so does the other
    thats an odd setup i'd say, but not totally unheard of, the point of a SAN is to abstract all that stuff, dedicating entire raid groups to a server seems a bit pointless, even if it is going to use all the space on it
    you carve up SANS at the LUN level really, not the raid group level

    so

    if all disks in a raid group are unusued, you can delete the RG and remove the disks, but i would actually qualify that is the case in the SAN management interface first, or you could s crew up data from the other server

    seriously though, i'd recommend keeping the SAN in tact, learn it, maybe improve it, but dont revert BACK to local disks unless you absolutely have to because of say, performance problems
     
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  8. Phoenix
    Honorary Member

    Phoenix 53656e696f7220 4d6f64

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    did this ever get sorted Si?
     
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  9. simongrahamuk
    Honorary Member

    simongrahamuk Hmmmmmmm?

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    Hey mate,

    No I haven't managed to get this sorted out yet, I've been away on a two day course, and today found out that I will be going full time at that site for six months to try and sort their systems and infrastructure out in the new year. It's all a bit up in the air at the moment as the guy that is in there at the moment has just found out that we're pulling him out and effectively 'demoting' him.

    It is one of my highest priorities to get sorted when I'm in the place though.

    8)
     
  10. Phoenix
    Honorary Member

    Phoenix 53656e696f7220 4d6f64

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    ok matey
    well keep me posted and ill help where I can when the time comes :)
    can probably even throw up a gotoassist or something :)
     
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  11. simongrahamuk
    Honorary Member

    simongrahamuk Hmmmmmmm?

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    Nice one Ryan,

    I'll hopefully be coming up with some plans for that place in the next few days, so may be in a better position then.

    8)
     

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