RAID Mirror and or Striping

Discussion in 'Hardware' started by BobbyMurcerFan, Mar 6, 2003.

  1. Is anyone using a RAID array to backup data (mirror) your primary hd or to (stripe) span files across hds for faster access?

    I've heard the stripe route is a little less stable--so it makes me hestant. However, mirroring seems like a good idea, esp. with a 2nd hd costing ~$100.

    What's your experience, thoughts? Thanks a lot.
  2. miniTrdr


    stripe will make your data 1/2 as reliable - if one drive fails you lose all data

    mirror improves reliability. the mirror could protect you from downtime and data loss but tape is more reliable for data protection.

    i just went thru a hard drive failure - my power supply went out and after replacing the power supply i found my harddrive was fried also. replaced drive and still having issues with that system. tape being offline would of protected my data. luckily i had a backup on CD but couldnt fit everything on it.

    so depends on what your trying to achieve - possible lower downtime & data protection or data protection.
  3. So if your PS fries your main hd, it's probably fried your secondary one as well. Have you looked into using DVD for back up? & which tape drives do you like? Thanks.

    P.S. could I do something where I have the 2nd hd archive the 1st one EOD and then have it dormant at all other times?
  4. miniTrdr


    i would assume the 2nd drive would of been toast if i had it.

    tape/cdr/dvd doesnt matter what you use - it depends how much data you have. you want to be able to back up all data without having to change CDs/tapes/etc. i got a deal on 12/24gb dat tape drive and a bunch of tapes. one tape will hold at least 2 full backups and 2 weeks worth of incremental changes without changing the tape (just backing up data not OS or programs).

    if you have the 2nd drive go and mirror it. just realize mirroring is for reliability and uptime not a backup solution.
  5. Using Raid in a trading workstation is a hard to justify case.

    Using Raid 1+0 might make it better, however, the implicit notion of using RAID is also coupled with other maintenance functions done regularly and offline.

    Some of those functions would be, as mentioned, creating either a current tape or CDR/DVDR backup mirror image of the primary drives. Without that, its just like running with a catch pan, and never doing anything with what's caught in that pan.

    RAID imposes a noticable overhead upon your op-sys and for those desiring of making screaming trading machines, I'd have to ask, what are you doing that you need such dynamic backup instead of periodic backups.

    For that matter, you might also look into running with dual drives not linked what so ever, or even daisy chained in a simple network onto another physical machine over an RJ45. Couple to this a basic disk drive utility that takes frequent and timely flash backups and synchronizes them. This allows for instantaneous recovery. There are many off the shelve software products offering these features. Talk to any competent technician at your local Office Depot, CDW, Staples or other software retail chain.

  6. Couple rules of thumb - never stripe unless you're also mirroring the stripe set and never stripe unless you're using multiple physical disk controllers (not drives, actual controllers) and don't using striping just to get a larger virtual disk drive (use bound volumes instead).

    Striping is for performance and you need more than one disk controller to take proper advantage of it (you're able to do parallel data transfers which is one of the underlying ideas behind striping). Usually striping is for servers rather than desktops. Although I have seen a couple video editing setups that used striped and mirrored disks.

    Mirroring is a simple, cheap, and low impact way of creating a degree of fault tolerance and under certain conditions getting a little extra read performance out of the storage subsystem. You don't need an additional controller to mirror (unless you absolutely want maximum fault tolerance) and it'll protect you in the event of a disk crash. Note that mirroring will NOT save you from accidentally deleting or mangling files because those operations will be mirrored in realtime.

    However, if you have room in your box - there is a way to using mirroring both for ongoing fault tolerance and for backup purposes. Install three disk drives. Set disk 1 as the primary and configure an initial mirror set of disk 1 mirroring to disk 2. At the end of the week, break the mirror set and re-establish the mirror of disk 1 to disk 3. Now disk 2 is a ready to go backup. You can either then back it off to tape, CD, or DVD if you want to, or just use it as a weekly rolling backup (depends on your needs). At the end of the next week, just break the mirror and re-establish the mirror of disk 1 to disk 2. Now disk 3 is the hot backup.

    With mirroring active, if you encounter a fault or crash on your primary disk, the mirror disk will automatically take over without causing a system fault. In addition, if you're doing a lot of reading from the disk during some process, the system can use the mirror as a secondary source to read from and can overlap head seek times or if you elected to install a second controller can do parallel transfers (although the performance improvement isn't as high as a properly configured stripe set, it can be worth up to 10%).

    Mirroring causes little or no nominal performance impact. No impact if you use a RAID controller because the mirroring operation is handled by the hardware. An almost unnoticable impact if you use software mirroring except following system reboot when the mirror disk must be completely regenerated, so there's a noticable CPU and disk subsystem slow down until the regen process completes. Note that you can still do normal operations without waiting for the regen process to complete because the mirror disk is high watermarked - however you won't have a fault tolerant disk environment until the mirror is completely regenerated.
  7. cevans


    Using Raid 5 (striping and mirroring) with 3 or more drives gives you the best of both...
  8. ZBEAR


    ArchAngel seems to know his stuff.

    I'm running two, 2 gig machines - each running 2 mirrored SCSI drives.
    I run Win2000 SERVER - because Win 2000 would not run "Mirror".
    I am told that XP Will run Mirror.

    I also have an "External" 36 gig SCSI that I fire up with the flip of a switch.

    I use it to back up some data , . ( and those all important MP-3 files ).
    It's esp. nice to take over to a friends house and DL all of their music.
    ( if they have a SCSI Card )

  9. Arch - excellent answer.

    Bobby - that explanation is one that a non-technical person can follow.

    The net problem for you is to decide what the machine is being used for, and whether or not you need those bells and whistles. He mentioned that servers and other high performance high throughput machines needed such instantaneous backup. If you consider your processing as such then you might benefit from such an array.

    Arch mentioned that dual controller cards were mandatory, and not using the daisy chain wire linkage for HDD #2, #3, #4 off the primary. This is a technical fact that most installers usually find out about after they can't achieve any significant backup after a crash. Excellent point to recall.

    A number of mother boards provide for Raid, whereas you used to have to add a controller dedicated to providing Raid. This is an improvement, however, go over a written diagram of your proposed system before purchasing dollar one, just to make sure that the details support what you think you're achieving.

    If this is for your primary desktop or workstation which you trade upon, then you have to ask, what are you really saving on your machine that needs such instant restoration, and whether or not you can't shunt that off to another cheaper box that's not subject to virus, infection or direct connection to the Internet or otherwise.

    Again, another consideration would be the instant file duplication processes that any competent (Diskkeeper) HDD management software provides.

    good answers - Arch
  10. Thanks for all the EXCELLENT replies!
    #10     Mar 6, 2003