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How do you do....it? Thread, You thoughts on a SAN. in Technical; Not to mention the iops available on a dedicated SAN solution, which is way in excess of a storage server. ...
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    Abaddon's Avatar
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    Not to mention the iops available on a dedicated SAN solution, which is way in excess of a storage server. It's about speed as well as resilience.

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    @zag a good quality, well implemented SAN is about as far from single points of failure as you can get, multiple drives with constant data shadowing and 10minute backup to disc schedules, multiple power supplies with UPS's (powered from separate circuits if not separate supplies if done correctly) multiple separate spine connections within the appliance, automatic failovers, multiple redundant connections to physical hardware... the list goes on!

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    may I recommend Pillar!

    Oracle and Pillar

    Oracle has just bought them

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    zag
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    46 VMs!!! wow yeh you are getting into datacenter territory there I have 16 here and thought that was a lot!!

    Basically what I'm asking is what if the SAN fails? Does it just auto repair itself like a RAID5 machine? Is it more reliable than a normal computer?

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    Quote Originally Posted by zag View Post
    Basically what I'm asking is what if the SAN fails? Does it just auto repair itself like a RAID5 machine? Is it more reliable than a normal computer?
    In an ideal world... you have two (possibly more) separate SANs, ideally in separate locations, and both of these SANs have dual redundant controllers/heads. The SANs will replicate data between them on a synchronous or asynchronous basis. The disk trays on the SANs will be running at least RAID5, more like RAID6 or RAID-TP (depending on their workload, you might have RAID10 for performance - my point is that there will be plenty of redundancy for failed disks) and there will be hot-spare drives available. Each controller will have multiple NICs with multihoming set up on them. The controllers and disk trays all have redundant hardware - dual PSUs, dual SAS controllers/cables, etc.

    If a disk fails - it'll rebuild the array using a hot-spare until the drive is replaced. RAID-TP would take three failures before you had any concerns.
    If a controller fails - it will failover to the redundant controller with zero (or very, very little) downtime.
    If a switch/link fails - multihoming or port trunking will ensure a route to the SAN is always available.
    If lots of disks fail, or you suffer a catastrophic failure to the SAN - you will automatically or manually failover to the replicated SAN with very little data lost (depending on your replication schedule).
    If data is lost accidentally - your SAN usually has snapshots which can be treated as an internal backup and will allow you to get data back if your normal backup strategy fails.

    In other words, if done properly you'll have no single point of failure. The above sounds complicated, but if you buy enterprise-level hardware then it should (not arguing with those using standard servers and rsync!) be simpler and more robust in the event of a major failure than trying to do the same with Windows servers or some kind of local storage.

    Chris

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    Quote Originally Posted by RabbieBurns View Post
    we went with HDS for our SAN, theyve been great and have a local presence which is handy..

    @zag, im at about 46 VMs, just now.. the SAN has 2 controllers, 2 switches, and 2x 2x10gb into the core, and each of these are spread over 2x UPS. As well as all the raid groups in the san there are also hot spares etc. I dont see where the single point of failure comes in?
    Corrupt firmware!

    Of course only if you mess around updating firmware.

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    Quote Originally Posted by Finch7 View Post
    Corrupt firmware!


    That's what the dual controllers/heads are for in theory. You should be able to update one, when you reboot it for the update to take effect it'll failover to the other head, you can then check the first head is running properly before bringing services back on to it, and if anything breaks when you do so you go back to the second head that's still on the original firmware. Like I said, in theory!

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    Depending on your SAN the controllers load balance and failover in different ways... our VNXe is active-active so I assign the datastores alternately between controllers... when we did a shutdown recently it failed over seamlessly to the other controller and back again.

    Out of that list the only part I don't have is a 2nd SAN (or 2nd building to house it in actually )

    Veeam does help there though as I then have a secondary copy of all the VMs that can run directly from backup so that helps. The only thing I'm not entirely convinced about on SANs is using file shares on them natively. When we got the VNXe I was quite excited by that feature as I never wanted to see a Windows file server ever again but unless you use the SAN replication backup becomes more trouble than it's worth so going to just stick with Windows VMs and Veeam as per the rest of the servers.

    Read an interesting point on PC Pro saying don't virtualise file servers but if the storage is on the SAN it makes little sense not to virtualise and take advantage of multiple host failover and not be reliant on physical server hardware for that role?

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    Quote Originally Posted by gshaw View Post
    Read an interesting point on PC Pro saying don't virtualise file servers but if the storage is on the SAN it makes little sense not to virtualise and take advantage of multiple host failover and not be reliant on physical server hardware for that role?
    I can only assume it's because you don't want the Windows overhead, plus the hypervisor overhead, then the SAN OS overhead when it comes to serving large amounts of files. That seems to be a lot of IP stacks to go through compared to sharing files straight from the SAN via SMB/CIFS. (definitely my preferred option when possible!)

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