RAID Questions

Discussion in 'OT Technology' started by mrmegabyte, Aug 16, 2008.

  1. mrmegabyte

    mrmegabyte New Member

    Joined:
    Sep 15, 2006
    Messages:
    26
    Likes Received:
    0
    I know a bit about Raid, but I am just wondering what types of Raid does everyone if you use it.

    I four 320GB hard disks and looking for the best way to set them up.

    I was thinking of Raid5 but then someone mentioned to me Raid 1+0 or Raid 10.


    What are your thoughts and experiences?

    I want performance, but want to make sure that nothing is lost.
     
  2. Chris

    Chris New Member

    Joined:
    Oct 27, 2003
    Messages:
    14,711
    Likes Received:
    0
    Location:
    Texas on my mind
  3. awns729

    awns729 New Member

    Joined:
    Jan 4, 2008
    Messages:
    353
    Likes Received:
    0
    Raid 5 will only use the space of ONE drive out of however many you have for parity information. Actually IIRC, it spreads parity information over all the hard drives in the RAID array, but all together you lose the equivalent of one drive of space. This guarantees you against failure of one drive, as it can rebuild the array through the parity information stored accross the array. This is the setup I would go with. I think write/read performance is a little slower than RAID10, but look that up to be sure.

    If I'm correct, the only upside to RAID10 is the slight boost in performance. The downside is that you have half your drive space lost. I think RAID10 has your data striped accross two drives (like RAID 0) and then its mirrored on the other two drives (like RAID 1). I'm pretty sure thats how it works, but you can double check.

    I would go with RAID 5. Or you can do a RAID 0 setup (one drive fails, lose everything), and use an external drive or another drive to make a backup of your important stuff. That's what I do in case I can't boot my computer for other reasons, at least all my stuff is on the external.
     
  4. HY

    HY New Member

    Joined:
    Dec 10, 2006
    Messages:
    57
    Likes Received:
    0
    raid 5 is going to slow down your writes but if your just going for backup or some other shit that is not write intensive its the best bet. reads should be a little bit faster then raid 0 but you will have more space.
     
  5. dissonance

    dissonance reset OT Supporter

    Joined:
    May 23, 2006
    Messages:
    5,652
    Likes Received:
    1
    Location:
    KS
    I run a RAID-5 with 5 320GB disks. I am in the process of getting it going with my new 1TB disks. Performance is noticably higher than just a single disk. As for comparing to other RAID levels I have never run any other.

    You may want to read this: http://dissonance.us/fusionowners/up/raid_performance.zip
     
  6. 5Gen_Prelude

    5Gen_Prelude There might not be an "I" in the word "Team", but

    Joined:
    Mar 14, 2000
    Messages:
    14,519
    Likes Received:
    1
    Location:
    Vancouver, BC, CANADA
    +1 for Raid 5. If you're really anal, Raid 5 plus hot spare.
     
  7. CyberBullets

    CyberBullets I reach to the sky, and call out your name. If I c

    Joined:
    Nov 13, 2001
    Messages:
    11,865
    Likes Received:
    0
    Location:
    BC, Canada/Stockholm, Sweden
    RAID 5 with SAS = the win.
     
  8. Harry Caray

    Harry Caray Fine purveyor of x.264, h.264 & TS HD-Video !!! HD

    Joined:
    Apr 19, 2001
    Messages:
    17,176
    Likes Received:
    5
    Location:
    MyCrews:4x4,SoCal,Tesla,EV's
    I pretty much run only RAID 6 (or RAID-DP) now but it only make sense for setups with 6 or more drives. 8 is the sweet spot.

    Run RAID-5 if you have some way of backing up or of the data doesn't matter.
     
  9. 5Gen_Prelude

    5Gen_Prelude There might not be an "I" in the word "Team", but

    Joined:
    Mar 14, 2000
    Messages:
    14,519
    Likes Received:
    1
    Location:
    Vancouver, BC, CANADA
    You'd be an idiot to be running RAID-6 and not backing up the data anyway.
     
  10. deusexaethera

    deusexaethera OT Supporter

    Joined:
    Jan 27, 2005
    Messages:
    19,712
    Likes Received:
    0
    RAID5 isn't going to slow down his writes; it's still splitting the data across multiple disks instead of just one, meaning each disk only has to handle part of the data, meaning the data gets written faster.

    RAID3, on the other hand, does slow down writes a bit compared to RAID5, but it's also a bit faster when reading data because all the parity is on one disk and it can be completely ignored instead of needing to be skipped over.
     
  11. deusexaethera

    deusexaethera OT Supporter

    Joined:
    Jan 27, 2005
    Messages:
    19,712
    Likes Received:
    0
    I like how we've gotten to the point where even RAID isn't safe enough -- only RAID with a hotspare is acceptable.

    For home use, a RAID without a hotspare is perfectly safe. Just make sure you use a plug-in controller so you can replace the controller with an identical one in case it ever craps out. Other than that, just pay attention if the thing tells you one of your disks is dead.
     
  12. Harry Caray

    Harry Caray Fine purveyor of x.264, h.264 & TS HD-Video !!! HD

    Joined:
    Apr 19, 2001
    Messages:
    17,176
    Likes Received:
    5
    Location:
    MyCrews:4x4,SoCal,Tesla,EV's
    who said that I 'was not' doing backups on my RAID setups? :ugh: :rolleyes:

    The point is, as drives get bigger, so do the bit-rate errors, and so do the rebuild times. RAID-5 is not the defacto anymore with only 1 parity. It was when 20-146gb drives were the rage....

    and 1-4hr rebuild times were a REALITY :rofl: but now, with 500-1.5tb drives, you have 8- 15 HOUR:eek3: rebuild times and during that time if ANY of that parity is bad or cannot be regenerated...

    BYE BYE DATA :hay: and you've gone from a "DEGRADED" state to a "FAILED"

    That's why EMC, NetApp, HDS, Pillar, etc,etc,etc,etc,etc,etc,etc,etc,etc,etc,etc,etc,etc,etc, are pretty much all using forms of RAID-6 / DP / dual rotating parity

    /thread
     
  13. deusexaethera

    deusexaethera OT Supporter

    Joined:
    Jan 27, 2005
    Messages:
    19,712
    Likes Received:
    0
    That's a valid point in theory, but nobody needs multiple terabytes in a single desktop computer, so if they have such a setup, they're a fool anyway.
     
  14. Harry Caray

    Harry Caray Fine purveyor of x.264, h.264 & TS HD-Video !!! HD

    Joined:
    Apr 19, 2001
    Messages:
    17,176
    Likes Received:
    5
    Location:
    MyCrews:4x4,SoCal,Tesla,EV's
    If no one needed multiple terabytes, then 1tb drives would only be avail for the enterprise.....

    I shoot all my DSLR 12mp photos in RAW format, all my HighDef video in 1080i... and just this weekend alone, took about 30gb of photos alone... haven't transferred the video yet.

    People have more need for storage now then ever... but can't back it all up..

    Goto the A&P forum and tell them what you just said :rofl:
     
  15. deusexaethera

    deusexaethera OT Supporter

    Joined:
    Jan 27, 2005
    Messages:
    19,712
    Likes Received:
    0
    They're available to end users because there's no reason to not make them available. That doesn't mean anyone needs them. What people need is to learn how to throw shit away after they've had it around for years and it's totally obsolete. I know people who are convinced that it's a bad idea to ever delete any files -- including their browser cache. There are two of them that I know, and they both literally have their cache size set to the size of their hard drives. Well shit, you never know when the entire Internet will crash and you'll be forced to browse your cache in offline mode, right?

    I never did understand why RAW format doesn't use non-destructive compression, like ZIP or something along those lines. There's simply no reason to waste all that extra space. Have you ever ZIPed a bunch of uncompressed images? They reduce in size by 50-67%.

    There's no point in going to the A&P forum and saying anything about computers, any more than there's any point in coming here and talking about the finer points of photography; just because they use computer technology to do their work doesn't mean they know the best way for that technology to operate.
     
  16. dissonance

    dissonance reset OT Supporter

    Joined:
    May 23, 2006
    Messages:
    5,652
    Likes Received:
    1
    Location:
    KS
    I agree that RAID-6 is better than RAID-5, the only issue is the price of a controller that supports it. I run a RAID-5 and am comfortable with the redundency it offers.

    BTW, my RAID-5 with 5 320GB drives has a rebuild time of about 1 to 1 1/2 hr, which in the scope of the drive life doesn't bother me too much (thats with only ~150GB or free space). The chance of 2 drives failing within that time period when they have a 1.2 million hour expected life time is quite slim (Seagate ES.2 drives). Plus, before they even get close to their expected failure time I will probably upgrades the drives anway.
     
  17. 5Gen_Prelude

    5Gen_Prelude There might not be an "I" in the word "Team", but

    Joined:
    Mar 14, 2000
    Messages:
    14,519
    Likes Received:
    1
    Location:
    Vancouver, BC, CANADA
    Because you went out of your way to state you needed to do so in RAID-5. Not my fault if you can't express yourself correctly via English.

    RAID 6 only works in 4+ drives, and a lot entry level controllers don't support it. If people get up to size of drives you're dealing with, then RAID 6 would be a better choice.
     
  18. HY

    HY New Member

    Joined:
    Dec 10, 2006
    Messages:
    57
    Likes Received:
    0
    it has to do with parity calculation, not the actual time that it takes to write the data to the disk
     
  19. deusexaethera

    deusexaethera OT Supporter

    Joined:
    Jan 27, 2005
    Messages:
    19,712
    Likes Received:
    0
    The parity calculation is irrelevant. Any RAID controller worth paying for has dedicated hardware to do XOR calculations, and dedicated hardware is so fast it'll blow your mind. There's no way the disks can deliver data fast enough to saturate the XOR processor.

    The main bottleneck is the slot the controller plugs into.
     
  20. dissonance

    dissonance reset OT Supporter

    Joined:
    May 23, 2006
    Messages:
    5,652
    Likes Received:
    1
    Location:
    KS
    I disagree (about the bottleneck). It is quite obviously the drives that are the main bottleneck. The controller and firmware do make a a difference as well (which includes the parity calculations/etc), but the by far biggest bottleneck is the drives.

    EDIT: Unless of course you are using a drive box full of $30k+ SSD drives..... then maybe I'd consider the bandwidth of the slot being the limitation.
     
  21. deusexaethera

    deusexaethera OT Supporter

    Joined:
    Jan 27, 2005
    Messages:
    19,712
    Likes Received:
    0
    I was thinking of older setups, dissonance. You're right that the newer card slots go much faster.

    In any event, the parity calculation definitely isn't the bottleneck.
     
  22. HY

    HY New Member

    Joined:
    Dec 10, 2006
    Messages:
    57
    Likes Received:
    0
    you correct, the actual 'calculation' doesnt take any time at all, but keep in mind that you have to perform a read on every drive to get the information needed for the calculation. this can be done in parallel, but even 1 read operation requires all the drives to seek, and then after that, the new parity data has to be written requiring another write in addition to the actual data.
     
  23. deusexaethera

    deusexaethera OT Supporter

    Joined:
    Jan 27, 2005
    Messages:
    19,712
    Likes Received:
    0
    You're right that when "real" data is written to the array, the whole stripe has to be read and the new "real" data has to be superimposed on it before the new parity can be calculated. However, most RAID controllers will cache recently-accessed data specifically to avoid having to re-read it again if it gets modified a few seconds later, which reduces the number of re-reads necessary under the conditions when it would be most damaging to throughput -- during sequential I/O.

    Random I/O, on the other hand, is so impacted by seek times anyway that it's hard for the speed to get any worse as a result of the extra step, and when the computer is processor-bound and isn't hitting the RAID very often, it doesn't matter at all if it takes a few extra milliseconds to complete a disk write.
     
  24. dissonance

    dissonance reset OT Supporter

    Joined:
    May 23, 2006
    Messages:
    5,652
    Likes Received:
    1
    Location:
    KS
    I was just reading some EMC information and came across 2 points mentioned about RAID-6...

    1. Rebuild time for RAID 6 ~10% longer than RAID 5
    2. RAID 6 has a disadvantage to RAID 5 and RAID 1/0 for small, random writes and system write bandwidth performance, but other I/O profiles are not affected as significantly

    Of couse these aren't standard across the board for all RAID-6 arrays, but thought I'd mention it.

    Source: "EMC CLARiiON RAID 6 Technology" published July 2007
     
  25. georgexi

    georgexi o.O OT Supporter

    Joined:
    Jul 13, 2005
    Messages:
    5,206
    Likes Received:
    0
    Location:
    PA
    how much are RAID controllers these days? i'm currently planning out building a media server. weighing out the pros/cons of running RAID vs non-RAID (external hds for backup), cost, reliability, blah blah blah

    so much junk out there to learn
     

Share This Page