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JBOD and RAID 0/5 Questions

Discussion in 'Storage & Backup' started by TRG.dOinK, Jul 25, 2011.

  1. TRG.dOinK

    TRG.dOinK Member

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    Not sure if this is the right spot to ask.

    I currently have a media player and I use two external USB drives which both are full (1 is dying :S).

    I need more space and my media player only has 2 USB ports, so buying another external drive is annoying having to plug in/out drives along with more power adapters etc. As time goes by, I can only see myself needing more and more space.

    So I'm looking at the Lian Li EX-503 external bay enclosure for something neat and small (NAS too expensive).

    I basically decided I need to choose between JBOD, RAID 0 or 5.

    I understand Raid 5 has parity files, so if one disk dies, I can still access data and replace the faulty drive with a new one, and that raid 0/jbod doesn't have any data protection/recovery. I also understand basically you loose 1 drives data in Raid 5 due to parity (repair) files.

    I don't entirely require RAID 5 as my mate will have the same setup/data, so we ourselves will be the backup so to speak. I would assume the likely hood of two raid 0/jbod failing at the same time would be minimal?

    I guess that leaves me to decide between raid 0 and jbod?

    My question with a RAID array is, can you "add" additional hard drives later on after you've created a raid array or do you have to create a new array in which it deletes/looses the current data when adding another drive?

    So say I bought 3x 2TBs, which keeps me happy with 6TB total, when its full, I cannot simply add another 2TB into a RAID 0 or 5 array without having to create a new array which intern deletes/removes the data, which then I'd need to copy the data again from my mate correct? Do the physical drives need to be the same model/brand?

    But I can add additional drives of any size/brand at any time if I go with JBOD without loosing any data correct? As I understand JBOD, its just multiple disks that show as one large disk. It fills the first drive, then onto the second, etc etc, so I don't see why you cannot just add additional drives when required which just increases the total storage without removing/deleting the current data?

    I guess if thats the case, thats a big advantage of JBOD over RAID 0, as I don't need to copy/paste everything over again if I need to create a new array due to adding HDDs/increasing space? How long would it roughly take if you were to create say a 8TB RAID 0 array, then copy/paste say 6TB of data via USB 3?

    Also, how do you know when a drive is failing/dying in one of these enclosure boxes? Do you run chkdsk on them or HD Tune etc? Can you select the individual drives when their set in a RAID array or JBOD and check the health status of each individual drive, or are there LED indicators on the box etc which are hardware controlled which show the status of the drives, or is there Raid/JBOD software you install etc to test each drive?

    I ask this because my silly external drive is coming up with "cannot read from the source file or disk" for certain files when I try to play or copy the file, chkdsk shows no issue, chkdsk /r states bad sectors, hdtune shows 2x warnings, yet I'd say 90% still read/copy fine (currently trying to backup as much as I can :p). I didn't know anything was actually wrong until I tried to copy the files, so in this case would a RAID/JBOD pick something like this up?


    Hope that makes sense, really tired, so late...
    Cheers.
     
    Last edited: Jul 25, 2011
  2. Menthu_Rae

    Menthu_Rae Member

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    * The EX-503 is a good unit.

    * In general, yes you can "grow" arrays. However, in the case of the EX-503 you need to use the configuration software to set things up (or the DIP switches on the back). I have not seen the ability to grow the array in the Windows software, nor can you do it from the DIP switches:

    http://www.lian-li.com/v2/tw/product/upload/manual/EX-503-UserManual.rar

    In this regard, if you add a drive or two - you would have to destroy the array and start again (make a new array with the new disk included and then copy all data back).

    You can get around this by running the EX-503 in passthrough mode and letting a software raid program like mdadm (in linux) or something else in Windows handle the configuration.

    * I'm not sure if JBOD can work in that way or not re: adding disks and it just increasing... hopefully someone else can shed some light here?

    * Yes you can add disks of any size/brand to a RAID array in general - however the array size will typically be a function of the number of drives minus the number of redundant drives, times the minimum drive size...

    i.e. Size of Array = {[No Disks - No Redundant Disks] * Smallest Disk Capacity}

    See wikipedia for more info... http://en.wikipedia.org/wiki/Standard_RAID_levels

    * Again I'm not sure for Windows/the JMicron software - but you can enable failure alerts using something like mdadm in linux. If the software is decent (you would hope it is) - it will alert you if a disk drops off the array, etc.

    It is always a good idea however to monitor and test the disks in your array - as well as running tests on your data if it is ultra important to you (catching corrupt files, etc). Running ECC RAM in your system (if supported) and having good quality cables and power supply is a good idea too.

    * In an 8TB RAID0 array, you would expect write speeds approximately n x minimum disk write. Where n is the number of disks. So if you have 4 x 2TB drives that typically write at say, 100MB/s - you can roughly achieve 400MB/s writes. Same goes for reads.

    Over USB3.0, if you have a good controller - you can expect SATA-like speeds. The theoretical max is 600MB/s. I haven't tested up to this level but I have found that running drives singularly over USB3.0 that the speed is similar to eSATA (i.e. no performance loss compared to plugged in internally).

    * If I were you, I would buy 5x 2TB drives, put them in RAID5 and be done with it. That gives you 8TB of usable space and then when the prices come down you can go and grab 5x 3TB drives and do the same.

    Note however that the rebuild time for an array of 2TB drives can be quite long - thus if you buy disks from the same batch then there is some likelihood that another disk could fail during rebuild time... in which case you are SOL. With JBOD you would just lose whatever data was on the disk(s) that died... So this is something to consider.

    Anyway yeah hope that answers a bit and hopefully someone else (with more windows experience) can jump in and give some advice to you, too.
     
  3. rowan194

    rowan194 Member

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    Your mate having the same set of "Linux ISOs" would take care of the backup side of things, but have you considered how much of a hassle it will be to copy the data back if a drive in RAID0/JBOD does fail? The advantage of RAID5 is that the array continues to work (with performance degraded) even after a drive fails. With RAID0/JBOD, any failure will instantly disable your array. In addition, there's a greater overall chance of failure with RAID0/JBOD because of aggregated probabilities. If one drive has a 2% chance of failure, will a four drive RAID0 have an 8% chance of failure?

    I'm not sure about your question on expanding JBOD, it would seem to make sense that it's possible since it doesn't require any rebuild or moving of data (at the RAID level - the OS still needs to grow the file system), but you'd need to be sure with that specific unit that it can be done.
     
  4. Madengineer

    Madengineer Member

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    with the Li EX-503 Are you able to just put seperate HDD's in it, No raid or JBOD? be able to read them as seperate drives? I've been looking for something like this so that i can put my extra internals into something.
     
  5. Menthu_Rae

    Menthu_Rae Member

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    Yes you can. It's how I run mine. :thumbup:
     
  6. OP
    OP
    TRG.dOinK

    TRG.dOinK Member

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    Thanks for the replies so far :thumbup:
    Surely theres someone on ocers that knows JBOD? :shock:

    Menthu_Rae,

    I can understand just buying 5x 2TB drives and setting in RAID 5, but I don't have 8TBs worth of data, so I can see it being a bit expensive having to buy 5 drives straight up plus the unit, and not actually using the space/data.

    I'd only need to buy 3 drives with a RAID 0, so hence my temptation to just go with it ($170 difference if I buy 5x, or $85 if I buy 4x).

    Even if I did buy the 4 drives in a RAID 5, if I filled the 6TBs of data, I'm going to have to redo it all again to add another drive (I wont be using some software to extend the array as I intend to mainly sit the unit beside the media player, would only be connected to the pc to copy stuff over, check hdd heath etc) , so if I go with RAID 5, I'd be buying the 5 disks. Hrmmm, decisions decisions....

    Also, since you stated the Li Lian can run as individual drives, how do you set that up? The manual doesn't state anything with the DIP switches etc? I assume you simply do not push in the "activate" button on the rear of the unit?

    Sounds like a great function, but I don't think it will work for my media player as I assume it will only find the first HDD, but would be really neat if it was beside a PC for data/backup, where you can easily add more drives/copy stuff to a certain drive etc, and not having to buy more external drives/power adapters etc.

    I guess I could run a XBMC media server or SAMBA, but then my PC would need to be on to access the data, which I don't really want.

    --------------

    rowan194,

    I have thought about the hassle part if a RAID 0 array failed, but say I had 3x 2TB drives, wouldn't you just simply set up the RAID 0 array again after replacing the faulty drive, then just copy/paste the data via eSata or USB3?

    Say each each drive can write at 80MB/s, that works out as 240MB/s x 60sec x 60min = 864GB per hour, so would only be around 7 Hours to copy over 6 TBs which isn't that bad.

    I'm just not sure if there is any time in actually "setting up a raid 0 or 5 array" etc?

    If thats the main hassle of a RAID 0 failure, it doesn't seem that bad? Its basically the same now as my single external USB drive, if it dies, I just have to copy/paste the data from my mate to the new external drive. Its annoying, but I can leave it overnight I guess etc...
     
    Last edited: Jul 25, 2011
  7. rowan194

    rowan194 Member

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    You may find that a low end RAID unit doesn't achieve array speeds anywhere near (average_drive_speed X number_of_drives). Some of them are so slow that the gigabit or USB2 interface is not the bottleneck! (And with the much higher potential speeds of USB3 or eSATA you may be sorely disappointed...)

    BTW, bear in mind that the speed of a JBOD will be equivalent to a single drive. JBOD is like a cascade, where once one drive fills the next will be used; RAID0 is like slicing and dicing with multiple streams for additional sequential read/write speed.

    Generally creating a RAID0 or JBOD array should be instant, but a RAID5 array may need to be initialised (basically a degraded array rebuild)

    Anyway, just putting it out there... if the data isn't really all that important that you can live without it for a night or two, it's not really an issue. :thumbup:
     
  8. OP
    OP
    TRG.dOinK

    TRG.dOinK Member

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    Hrm alright thanks mate.

    Yea I've basically ruled out JBOD due to the speed of only 1 drive at a time, compared to multiple with raid 0. Would be much slower to copy/paste everything if a drive died with JBOD :S

    So now I'm back to either RAID 0 or 5, so I'm getting there slowly :p

    I guess I'll need to check reviews on the Li Lian 503 for RAID performance then? Would be disappointing if it was only doing 20MB/s etc, hrm, any reviews around, or anyone have one of these boxes set as a RAID 0 or RAID 5 array and can tell me their speeds? Maybe I should be looking for a review of the chipset?
     
    Last edited: Jul 26, 2011
  9. Menthu_Rae

    Menthu_Rae Member

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    If you can wait a little while I can maybe do some benchmarks for you next week sometime?

    I really want to help out the community as I'm the kind of person who enjoys putting information out there especially if it doesn't exist or is scattered all over the place/poor quality... unfortunately atm there is just so much stuff going on in my life and I also don't have any spare hard drives to run the benchmarks on :upset:

    But yeah if you can wait another week or so I should have 4x 1TB disks to do some benchmarks with... I can test e-SATA and USB3.0. :thumbup:
     
  10. OP
    OP
    TRG.dOinK

    TRG.dOinK Member

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    Yea would be good if its not any trouble.
    Also found this review here with the same chipset
     
  11. samos

    samos Member

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    OK, another question for you fellas:

    How long does it take to rebuild a RAID 5 setup (5x 2TB) if one disk fails?

    I've googled a bit, but getting various answers from 3 hours to 2 days.
     
  12. fang_laluna

    fang_laluna Member

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    Sorry, don't mean to hijack thread.

    I've got a question still related to EX-503 AND RAID 5. Does this unit's SATA port multiplier works with e-sata Intel based motherboard (Raid 5 setup)? I have EX58-UD5.
     
  13. OP
    OP
    TRG.dOinK

    TRG.dOinK Member

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    Since only 1 drive needs to rebuild its data in a RAID 5, say 80MB/s write for the single disk, would it be....

    80MB/s x60 x60 = 288GB per hour
    2000GB / 288 = 6.94 Hours

    ??

    For a Raid 0 with 5 drives, 80MB*5 = 400MB/s
    400MB/s x60 x60 = 1440GB per hour
    10,000GB / 1440 = 6.94 Hours

    All theoretically though, as one would expect RAID 5 to be slower due to parity calculations etc correct?
    ----

    So if I were to do a RAID 5 it would still take the same time to repair the array, as to simply do a RAID 0 and copy/paste the entire data again?

    Maybe I might choose RAID 0 then, might take slightly more time/hassle to go to mates etc, but you get the extra 2TB drive space.

    Can you still use the RAID 5 array when its in the rebuild process?

    Does the array rebuild itself inside the EX-503 unit itself, or would I need to connect it to the PC, run the software and click repair or something?
     
    Last edited: Jul 31, 2011
  14. davros123

    davros123 Member

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    fwiw, it depends upon the setup.

    my reasonably beefy quad core pc with mdadm raid5 with 7 or 8 drive array was running at ~20MB/s (with peaks @60MB/s) ...so a long time at that rate.

    Now with zfs raidz2 on the same hardware, rebuilds are mucho faster (closer to 600MB/s).

    ymmv. I do not have any experience with hardware raid.
     
  15. rowan194

    rowan194 Member

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    Yes, that's the whole idea of it. :) Read operations will run slower as the controller has to access all the drives to fill the "hole" left by the missing drive, but the array itself is still logically intact and available for use.
     
  16. OP
    OP
    TRG.dOinK

    TRG.dOinK Member

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    Yea I understand you can still use it when 1 drive dies, I just wasn't sure if you could use the array when a new drive is plugged in and rebuilding, cheers :)

    Now just need to find out if the Lian does the repair automatically without having to connect to pc or use software etc. If you just pull out faulty one, put in new one and it starts rebuilding, thats sweet :) however, I'm not sure if thats the case?
     

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