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Hardware Thread, SAN advice in Technical; Must admit I haven't really heard of Coraid, but on paper that certainly looks good. 16 disks, minus two hot ...
  1. #16
    Duke's Avatar
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    Must admit I haven't really heard of Coraid, but on paper that certainly looks good. 16 disks, minus two hot spares in RAID 6 would give you about 11TB usable after formatting.

    My only concern would be the performance of 7.2k SATA disks - what RAID are you planning to use? 14-16 disks (depending on hotspares) in RAID 10 should give you perfectly good performance with around 7TB usable.

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    I was thinking of using RAID6 is this would give me better redundancy than RAID10 and I lose less disk space but RAID 10 is quicker right?

    I asked about SAS disk instead of the SATA ones and the consultant said the speed difference would only be small and for the extra cost they didn't think it would be worth it?!?!? I suppose I could get a quote with SAS disks in and see what the price difference is

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    Duke's Avatar
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    RAID 10 should be noticeably faster, and if the box has limited RAM or no flash acceleration it may be worth it. Rebuild times with RAID 10 would be fairly good I'd think (can anyone confirm?) so with a hotspare your redundancy isn't too bad. RAID 6 is only a benefit over RAID 5 if two disks fail at once, or a second disk fails during the rebuild. RAID 10 can in theory give you better redundancy than that:

    All but one drive from each RAID 1 set could fail without damaging the data. However, if the failed drive is not replaced, the single working hard drive in the set then becomes a single point of failure for the entire array. If that single hard drive then fails, all data stored in the entire array is lost.
    RAID 10 redundancy kind of depends on which disks in the array happen to fail.

    EDIT: See what prices they give you on 10k or 15k SAS disks. They should also be able to provide you with some ballpark IOPS figures on various workloads.

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    FatBoy (18th May 2011)

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    Quote Originally Posted by Duke View Post
    They should also be able to provide you with some ballpark IOPS figures on various workloads.
    Thanks for this Duke diamond advise and backs up what I have been reading and makes everything clearer. I have been looking up these IOPS figures and yes it looks like it might be a good idea to get the difference in figures between SATA and SAS

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    Duke (18th May 2011)

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    Quote Originally Posted by FatBoy View Post
    I have been quoted for a Coraid SRX2800-G SAN
    Six 1GigE Ports
    36 disk bays for 3.5" SATA, SAS or SSD drives
    with 16 coraid 1TB 7.2 SATA HDDs installed
    The SRX2800 has 16 bays not 36, so it would be fully populated.

    We're running a SRX3200 with 12 1TB SATA disks to provide storage for VMware vSphere. I tested all the available RAID schemes on the raw storage and found them to be fairly similar in read speed but RAID 5 gives the fastest write speed. RAID 10 is the slowest, given the same number of disks, so unless you need that level of redundancy I wouldn't consider it.
    Last edited by keithu; 18th May 2011 at 12:15 PM.

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    Thanks for the heads up on the disk bays keithu I'll have to check that out asap. I am surprise with what you said regarding speed of the raid arrays tho.

    I was sure RAID10 was in some way (write I think) faster than RAID5 because it doesn't have to deal with parity??

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    Duke's Avatar
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    Quote Originally Posted by FatBoy View Post
    I was sure RAID10 was in some way (write I think) faster than RAID5 because it doesn't have to deal with parity??
    I thought RAID 10 benefited from faster reads (the mirroring and striping both help, it's based on the number of disks) and faster writes (just the striping here based on number of disks - the mirroring shouldn't slow it down much though as it's just sending the same data to both sets in the mirror).

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    Quote Originally Posted by keithu View Post
    The SRX2800 has 16 bays not 36, so it would be fully populated.

    I tested all the available RAID schemes on the raw storage and found them to be fairly similar in read speed but RAID 5 gives the fastest write speed. RAID 10 is the slowest, given the same number of disks, so unless you need that level of redundancy I wouldn't consider it.
    Are you sure you've got that the right way round? Raid 5 is generally the slowest to write and Raid 10 generally one of the fastest of the truly redundant raid levels....

    Butuz

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    Quote Originally Posted by Butuz View Post
    Are you sure you've got that the right way round? Raid 5 is generally the slowest to write and Raid 10 generally one of the fastest of the truly redundant raid levels....
    Yes, I'm sure. With a fixed number of disks in the array the stripe length on the RAID 5 setup is almost twice the length of the RAID 10 and more than compensates for the overhead of parity writes. RAID 0 is faster of course, although I wouldn't classify that as RAID.

    I was testing with a multi-threaded client reading and writing 10s of gigbytes in 8k blocks; A different load might give different results.

  12. #25
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    Strange almost all documentation states RAID10 should be faster, I guess it depends on what tests you do and how it works in real life situation. Either way I think I know what I'm going to do now if the price is right...

    The CoRAID SRX3200 - 24 Disk High Performance Ethernet SAN Array
    With 16 disks in - 8 1TB disks and 8 2TB disks
    Setup 2 arrays one 8 disk array with the 1TB disks and the same with the 2TB disks
    Both RAID5 with 7 disk in the array and 1 hot spare
    The 1TB disk array I'll use for VMWare servers and a file store
    The 2TB disk array I'll use for backups and less important file store if needed.

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    Quote Originally Posted by dhicks View Post
    I still can't quite figure out why everyone is so obsessed with having their disk storage loosly coupled to their VM instances as if you're all running Amazon-scale datacentres, but if you're going to buy a SAN then the QNAP devices seem to be good value for money. Ours seems to be coping with being both an iSCISI target for Xen Server VMs and an SMB file server - you can at least save one lot of network traffic by having SMB traffic go straight to your storage server, rather than to a VM acting as a file server and from there to the storage server over iSCISI.
    Exactly. The first question is not what performance does x,y or z's SAN offer but what performance do we actually need. Schools seem to be spending a fortune on expensive devices they don't actually need.

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    Hi there. I know a fair bit about the S7xxx range from Oracle. give me a call to chat about VMs and iSCSI / NFS on our entry level storage devices...

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    Looking at the CoRAID website they only have a very small presence in the UK. I'd personally be worried about ongoing support and what happens if they decide the UK market isn't for them. You'd be left holding a SAN with nowhere to go....

  16. #29
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    I have been reading up on CoRAID and there ATA over Ethernet and its quite impressive, if anyone else is interested have a read of this SNS Europe February 2011 start on page 14-15, its a good read. Also Bruce Almighty drives Coraid AoE plan after $10m investment ? The Register

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