To Raid or not to Raid? (1 Viewer)

wazm

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    Hi, I am after a bit of advice.

    I have a Gigabyte GA-MA78G-DS3 motherboard and in preparation to move to Win 7, (awaiting the Release candidate), I have purchased 2 new Samsung 1.5 TB drives. Is it worth while to mount them in a raid configuration? I have 4 DTV cards and 1 Twinhan Sat card and the idea of having 1 3TB hard disk to save to does seem like a good idea but is there any performance gain to be made?

    Warren :confused:
     

    Scythe42

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    There's no real performance gain using a stripe set (RAID 0) in a HTPC setup with an onboard RAID. And if one HD fails the whole array will fail and you lose all data. You should never ever use a stripe set. One HD defect and everything's gone, probably your whole media library.

    It's better to use stripe sets with parity (RAID 5 or 6), so your data is protected for one or two HD failures at the same time. But never do this without a dedicated RAID controller (aka hardware RAID) as the performance impact will be huge as the CPU has to do everything or most of the work. Only an option if you really have CPU power to spare (example an older PC configured for NAS usage).

    General rule: onboard RAID = software RAID (except for a few very pricy MBs).

    The only difference is that the BIOS will know about the RAID array and you can boot from it. Booting form software RAID 1 (Mirroring) is always possible even with no BIOS support.

    RAID 1 (Mirroring) on the other hand can be used with an onboard controller to provide redundancy for the boot drive and it's the preferred home solution of a software RAID. Of course there's some performance vs. redundancy thing here when using software mirroring.

    Even though other RAID levels might be supported please stay away from them (and always stay away from RAID 0). It's not worth it from my experience.

    If you just don't want to deal with a lot of drive letters I recommend just mounting each of your old HDs as a sub directory in another directory. There's no need for using one drive letter of each HD anymore since a lot of years. For the Boot Disk you could opt for Mirroring though.

    PS: Standard RAID levels - Wikipedia, the free encyclopedia
     

    wazm

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    There's no real performance gain using a stripe set (RAID 0) in a HTPC setup with an onboard RAID. And if one HD fails the whole array will fail and you lose all data. You should never ever use a stripe set. One HD defect and everything's gone, probably your whole media library.

    I was only going to use it for the recordings and I guess losing them wouldn't be the end of the world.

    General rule: onboard RAID = software RAID (except for a few very pricy MBs).

    Fair enough. I was mainly after performance and I guess grouping of the drives into 1. Drive letters are not really a problem. I presently have a few 500gb drives and I am finding that one drive seems to take most of the recordings (as it is connected to the first priority TV card which cops most of the recording), and the others seem to be fairly empty most of the time.

    If MediaPortal chose a TV card at random or sequentially then the data may be better spread across the drives. I was hoping to achieve that by using raid but if it is going to be a performance hit then it isn't worth the trouble.

    Thanks for getting back to me so quickly with the answer. Much appreciated :D
     

    Scythe42

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    If you don't really care about data loss than RAID 0 is of course an option. I still don't recommend it unless you really just use it as a "scratch" disk and never put stuff on it you want to keep.

    From experience, sooner or later you run out of storage and put something on this array only "temporarily". Then it stays there forever and *boom* the array is gone. Been there, done that. :p

    Reading/Writing will be spread across the HDs and should give you a bit better IO in theory here but the cost is that the CPU will be more involved. Not so dramatically in a RAID 0 than a RAID 5 though. And it largely depends how good the chipsets handles IO to different drives at the same time. From my experience with onboard RAIDs not very good unless the drives are really slow in general. With some old slow HDs there can be a small benefit.

    But video streams don't really require that much IO performance as you can stream them over networks easily. But for your "scratch" disk approach it may be worth a try if you're running into IO performance issue. How about trying some benchmarks before you finally decide?

    For just grouping drives you could also go for a Volume Set in Windows, which basically concats the drives. Once a drive is full the next one is used. This has no impact on CPU or IO. Again not really fault tolerant but shouldn't be as bad as a stripe set if I am not mistaken. I think only data on the actual failed disk and data spanning across disks is lost.

    For some kind of "scratch" disk this could also be an option.

    But anything other than RAID 0 or 1 will have a significant performance impact on the CPU.
     

    wazm

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    Spanned volume set may just be the way to go then. It will address the problem I am having and there should be no noticeable CPU overhead, as far as I can determine that is. Raid seemed like it would be a good option but as you said, the chance of failure would mean total loss of data, and from reading, the chances of disk failure are doubled.

    Thanks again for your help! :D

    Warren
     

    pilehave

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    I don't get it? You get 3 TB of data-storage for recordings (that's like a gazillion recordings) but you don't care if they get lost?

    :)
     

    wazm

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    I don't get it? You get 3 TB of data-storage for recordings (that's like a gazillion recordings) but you don't care if they get lost?

    :)


    Most of them are the kids recording cartoon network etc :) Important stuff I copy off (my stuff) :D
     

    moab

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    I currently have a hybrid RAID 0 set up.

    C: is 32GB SSD contains OS + APPS.
    R: is 3 x 500GB RAID 0 using onboard Intel ICH8.
    E: is 1.5TB drive for backups.

    Initially I only had the 3 RAID drives.
    I ran some HDD benchmarking to test the RAID0 as I added 1,2 and 3 drives. For me it improve disk i/o by a factor of 1/n (n= number of drives) which is as one would expect e.g. 2 drives halves the read times, 3 drives one third read time.
    I did not record the CPU usage during i/o as it appeared to be negligible. With hindsight it would be interesting to see the comparisons.

    Then one day to my horror my OS got corrupted which prompted the addition of the E: as insurance. I had turned off disk caching in the RAID software which is risky if you turn the PC off without a gracefull OS shutdown. So don't turn it off. Naturally I have a UPS which is a must have item but someone turned off the PC using the power button due to it hanging.

    I was then the happy recipient of the SSD. So now my RAID is only used for DVD images, TV recordings and TimeShift. Disk i/o is fast and I have no performance issues other than mounting the iso image to virtual drive.

    I agree that RAID 0 is risky but if you can live with the risk then the performance gain is attractive.
    Performance gain is an 1/x factor increase. So the gain reduces as you add more drives. 2 drives = 50% 3 drives = 33% etc so diminishing returns.
    If you add a new drive to RAID array then remember that you need to re-build the array i.e. (re-install). I don't trust the hot adding to arrays in these low end RAID controllers as it just band aids the striping.
    Consider purchase of a $100 32GB SSD - blazing performance and reliable. Probably need a bigger SSD for Vista/W7.
    Note that for me the 1.5 TB performed about equal to the 3 x 500GB drives in RAID 0. After a certain point disk i/o is not a bottleneck.
    In your situation I would add an SSD and use the 2 drives as non-RAID and only for data. Easy to expand, less risk, best hybrid performance.
    The only reason you would want better performance is gaming or other disk i/o intensive activity.
     

    wazm

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    H Moab, I have a new samsung 500gb drive for the operating system so that shouldn't be a problem. The 2 1.5tb drives are to be used for time shifting and recording only. have you noticed any improvement in write times? eg: timeshifting?

    I don't know anything about SSD drives but I just had a look at some prices and they stary at $145 here with the first one in stock is a " Team 32GB 2.5" SSD, Combo SATAII, MLC (TG0032GS25AC1M) ". Does this mean it just plugs in as a Sata drive? Very worth looking at if it does as it should save load times.
     

    Gixxer

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    wazm you sound very worried about disk performance for timeshift and recordings. what numbers are we looking at ? how many recordings + timeshifts at the same time ? I think thats the first thing to have in mind, and then once set the target, look how to get to it.

    I say this cause time ago, i was recording 5 or 6 DVB-T SD at the same time, I was using a very old amd with an IDE 320gb drive.
     

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