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  1. #1
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    Question RAID 1 or HDD mirroring

    I am looking for Backup Utility . Came across this two terms

    Are RAID 1 & HDD mirroring synonyms ???

    Which is better RAID 1 & HDD mirroring ???

    Thanks in advance for inputs

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    Suraj jain
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  2. #2
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    Hi,

    A RAID1 setup is actually one disk that makes a mirror of the second one.
    This is mostly setup in software or hardware RAID and the second disk has exactly the same copy as the first one.
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  3. #3
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    Raid 1 is hdd mirroring
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  4. #4
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    technical diff between RAID 1 or DISK MIRROR

    Quote Originally Posted by ServerBoost View Post
    Hi,

    A RAID1 setup is actually one disk that makes a mirror of the second one.
    This is mostly setup in software or hardware RAID and the second disk has exactly the same copy as the first one.
    So is there any technical diff between RAID 1 or DISK MIRROR.. from your reply it seems both do the same task - EXACT COPY OF DATA
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  5. #5
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    RAID 1 is disk mirroring. If you have two hard disks set up as RAID 1 then any data written to one drive is also written to the second drive (mirroring).

    While RAID 1 is good for preserving data during a disk crash (if one disk crashes the system will continue to run with the other disk), it is *not* a substitute for backups.

    If you delete a file from a RAID 1 mirror set, that file is deleted from both drives. If you have backups then you could retrieve that file. So a good strategy is RAID 1 mirroring with backups.
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  6. #6
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    * HDD for RAID and MIRRORING

    Quote Originally Posted by msherman View Post
    RAID 1 is disk mirroring. If you have two hard disks set up as RAID 1 then any data written to one drive is also written to the second drive (mirroring).

    While RAID 1 is good for preserving data during a disk crash (if one disk crashes the system will continue to run with the other disk), it is *not* a substitute for backups.

    If you delete a file from a RAID 1 mirror set, that file is deleted from both drives. If you have backups then you could retrieve that file. So a good strategy is RAID 1 mirroring with backups.
    Thanks for input .........

    So these means i will need total 3 HDD for achieving "RAID 1 mirroring with backups" .

    Any suggestion : which type HDD are good for RAID and MIRRORING.
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  7. #7
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    For a mirror (raid1) setup you only need 2 disks
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  8. #8
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    Maybe you are referring with disk mirror some utilities that makes an exact copy of your HD when you execute the software, RAID1 works automatically, when your hd writes the new information in sectors also do the replication at the same time in the 2nd HD.

    Raid1 works fine but you loose some speed...

  9. #9
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    Like others have said, RAID 1 is the technical name for HDD mirroring.

    To clarify a couple things though:

    RAID 1 writes at the speed of a single disk, there is no speed penalty (assuming the drives are set-up correctly on separate controllers).

    RAID 1 reads at speeds higher than a single disk, especially for random read patterns. This is because the read request can be split between the drives.

    A lot depends on the RAID controller though, always use a hardware RAID controller from a reputable vendor (3ware, Adaptec, etc).

    As far as backups go, you can't rely on RAID. RAID is for uptime, backups are for data security. If your system is hacked, or infected, or data is corrupted it affects the data on both drives of the mirror thus you lose your data even though your drives are physically okay. Offsite backups are best, or at least off-system (onto a NAS device, tape, etc). You can install a third drive and use it as a backup but you lose the advantages of offsite in that situation and a hacker or virus could potentially delete them. Some RAID controllers support adding a third drive to a RAID 1 configuration, and once the third drive is rebuilt (sync'd with the other two) it is then removed, unmounted, or disconnected between backups.

    Here's a good RAID levels reference: http://en.wikipedia.org/wiki/Standard_RAID_levels
    Last edited by eviltechie; 04-02-2008 at 08:43 AM.
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  10. #10
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    Quote Originally Posted by surajkala View Post
    Any suggestion : which type HDD are good for RAID and MIRRORING.
    High RPM drives are always better, but they are more expensive and generally smaller (storage wise).

    Price not being an object, I'd go with 15,000 RPM SAS (serial attached SCSI) drives.

    A bit more reasonable option is 10,000 RPM Western Digital Raptor SATA drives.

    Note: SAS RAID controllers (and SAS controllers in general) can use SATA drives. So, if you got a SAS RAID controller you could start out with the cheaper SATA drives and upgrade to SAS drives when the budget permitted, without the need for a new RAID controller. This doesn't work in reverse though, SATA controllers CANNOT use SAS drives.
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  11. #11
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    Frankly, I wouldn't recommend RAID1. It's slow
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  12. #12
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    Quote Originally Posted by animedistro View Post
    Frankly, I wouldn't recommend RAID1. It's slow
    Slow? How do you figure?

    No other RAID level provides the balance of data redundancy, read/write speed, and low cost of entry that RAID 1 does.

    RAID 10 would be faster in all respects, but requires a minimum of 4 drives, and most 1U rackmount cases cannot hold 4 drives.

    Basically, if RAID 1 is slower than a single drive you're doing it wrong.

    RAID 1 is a perfect solution for low cost, no performance loss hard drive redundancy.

    RAID 10 would be great for higher-end servers, as it provides significantly better performance than a single drive on both reads and writes.
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  13. #13
    I wud suggest backups off the data centre itself...
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  14. #14
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    two raid 1 hdds is always slower than a single hdd for us, no matter linux software raid or 3ware hardware raid card, but hardware raid 1 does provide redundancy though.

  15. #15
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    What type of drives are they? What is the configuration? One drive per controller, shared controller, etc?

    In a suboptimal configuration RAID 1 can be slower, especially at writes. But reads should still be fast(er) for random access (sequential access slows to near single drive speed though). Slow configs could be a result of sharing controllers, fragmentation, low-end controllers, etc.
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  16. #16
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    tried seagate and WD sata2 drives, same results. we thought reads would be faster, but turns out it's pretty much the same, atleast the read+write overall result is slower than a single hdd. we use 3ware raid cards, i don't think they are low-end cards.

  17. #17
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    Quote Originally Posted by meyu View Post
    tried seagate and WD sata2 drives, same results. we thought reads would be faster, but turns out it's pretty much the same, atleast the read+write overall result is slower than a single hdd. we use 3ware raid cards, i don't think they are low-end cards.
    Not sure what you are using but the results aren't right

  18. #18
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    we are using 3ware 8006, 9500, 9550. if you guys seeing speed gain on raid 1 using those cards, may i ask what configuration you are using? btw our servers are used for php+mysql hosting, not sure that would make difference or not.

  19. #19
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    All of this is really dependent on the controller that you use. Most of the specific cards I have seen mentioned are only SATA I.

    Using a card that supports SATA II, uses a PCI-E bus connection, has plenty of onboard cache and using drives that will support these functions will give you a very nice solution.

    An example for this type of card would be something along the lines of a 3Ware 9650SE.
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