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Thread: RAID Arrays

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    3 Star Lounger E_OGRADY's Avatar
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    RAID Arrays

    I thought I understood a little about RAID and had decided on RAID 5 made up of two 200Gbyte disks striped a total of 400 Gbytes then with a 400 Gbyte drive mirrored. On searching the web it appears that RAID 5 is the way to go, but then I have read RAID 10 is the only one that gives the results.

    I want to stripe and mirror which RAID?

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    Plutonium Lounger
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    Re: RAID Arrays

    Each RAID option has it's own advantages and disadvantages, and often the one that works best depends not only on your data access patterns but also on the particular RAID implementation that you have. The levels that are generally thought suitable for a home PC are:
    <UL><LI>RAID 0 - also called striping. uses 2 or more disks, spreads your data across them, gives good performance but the failure of any disk loses all the data. The available storage space is equal to the total space on the 2 disks.
    <LI>RAID 1 - also called mirroring. uses two disks and stores all the data on both of them. If a single disk fails then your data is still available. The available storage space is equivalent to a single disk.
    <LI>RAID 5 - uses three or more disks, spreads your data across all the disks to give increased performance and includes sufficient extra information that your data is still available if a single drive fails. The available space is equal to the space on all the disks less 1 (e.g. for a 7 disk RAID 5 set you get the space of 6 disks).[/list]RAID 10 is not normally used for a home PC. It uses at least 4 disks, but 50% of the space is used for redundant information. It has very good performance and reliability.

    There's quite a good tutorial on the advantages and disadvantages of each RAID level here.

    StuartR

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    Re: RAID Arrays

    I use SmartComputing.Com when I refer clients to start Raid Arrays. Some good basic articles are:

    How To Insatll RAID 0

    How to Install RAID 1

    How To Install RAID 0+1

    How To Install RAID 5

    The General Search is here

    Unfortunately, The RAID 10 article I wanted to reference has a "Subscription" required.

    CoputerPowerUser.Com has an excellent article on RAID Workshop Four Array Types Built To Order which talk about RAID 0, 1, 5, and 10 and compare performance against a single drive. You can get a Web Only subscription fro $17/Year, but available to US/Canada only. <img src=/S/frown.gif border=0 alt=frown width=15 height=15> <img src=/S/razz.gif border=0 alt=razz width=25 height=17>

    <hr>but then I have read RAID 10 is the only one that gives the results.<hr>
    I'm not sure exactly what you mean here, but remember, RAID 10 requires a MINIMUM of Four (4) Hard drives of the same size (preferable). From the above article, a UPS was also recommended.
    Scott

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    Re: RAID Arrays

    CORRECTION - International Readers can also get the Web Only Access for $17.00/Year (USD).

    I noticed StuartR manged to post before me - he provided some excellent <img src=/S/free.gif border=0 alt=free width=30 height=15> references.

    With the Exception of the RAID Workshop article I mentioned in my post, the others are also <img src=/S/free.gif border=0 alt=free width=30 height=15>.
    Scott

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    3 Star Lounger E_OGRADY's Avatar
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    Re: RAID Arrays

    Thank you for the replies. I have succeeded in confusing myself.

    I need advice, I want to ensure the data on my new system. I have tried disk imaging and find it leaves a lot to be desired. (Explained in a previous post) I cannot get Acronis to span across DVD's. I lost my system a year ago with 6 backups or images when the time came none worked. Hence my interest in RAID.

    Having read the attached links it appears that maybe I am better off going to RAID 0+1. Would you agree? The cost of HDD's is low. The trauma of just copying data and reloading is daunting? I will be 70 next year, I have trouble remembering where original CD's are, not to mention downloaded software e.g. where Acronis is stored.

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    Re: RAID Arrays

    In my opinion RAID is not really needed on most home PCs. This is because:
    <UL><LI>RAID only protects you against hardware failure of a disk drive. Not against software failures or corruptions, or even hardware failure of a disk controller unless you have a very expensive setup
    <LI>Software errors and corruptions are much more frequent than hard disk failures
    <LI>You need to do backups to protect your data anyway, and these backups are also good enough to protect you against disk drive failure
    <LI>For a commercial operation with (e.g.) 5000 disk drives, they can expect to have drives fail every week, so RAID is worthwhile. For a home user with 2 or 3 disk drives they may never see a drive failure
    <LI>RAID is pretty complex, and is very hard to test to ensure that it will recover when it fails. Recovery requires well documented and tested processes, it is very easy to lose all your data if you do the wrong thing after a disk has failed in a RAID set.[/list]If your backup regime is no good then let's help you fix that, then you will be protected from all sorts of failures.

    If you absolutely insist on using RAID then my personal preferred configuration is to use RAID 1 for your boot disk (have a mirrored disk that you can boot from if the first disk fails) and then use RAID 5 for your data, with 3 or more data disks all of the same size and the data striped across all of them. Don't use Software RAID, make sure you have a high quality disk controller that has a good hardware RAID implementation.

    regards,

    StuartR

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    3 Star Lounger E_OGRADY's Avatar
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    Re: RAID Arrays

    Thanks StuartR you have brought my understanding up a few notches. In over twenty years I have only lost my system once through a hard disk failure. Fortunately it was the boot disk, fortunately I do not keep data in that area only system.

    I have two HDD's

    C: System
    E: Major Apps
    F: Minor Apps
    G: Data

    D: Data Backup
    H: Work Area

    As it turned out I was able to recover most of the data. Presently I make "Dual-Layer" direct copies of my data disk and the area on the H: drive where I maintain downloaded applications and patches.

    As an aside do you agree with static or dynamic disks?
    Does RAID take into account partitions on the drive? What I am trying to say is does RAID (say) image the physical disk or the partitions?

    Again my thanks for the education, I spent all day yesterday reading everything about RAID I could find on the web.
    The demonstration at http://www.intel.com/design/servers/buildi...s/demo/RAID.htm was the clue that gave me the horror thought that it was only hardware protection as you have confirmed.

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    Re: RAID Arrays

    RAID can be done either at the Physical Disk Drive level or at the partition level.
    RAID can be implemented in software or in hardware.

    If you have hardware RAID, implemented by the disk controller, then it cannot "see" partitions, and will apply to whole disks
    If you have software RAID, implemented by the operating system or an application, then it will typically be at the level of individual partitions.

    Hardware RAID tends to be more reliable, with higher performance, and easier recovery after disk failures. I would not recommend use of software RAID except in very special circumstances.

    I have never seen the benefit of dynamic disks for home users. They have a number of disadvantages, for example image backup products often can't back them up or restore them correctly, but few benefits. For a corporate server with NAS or SAN based disks the advantages may be significant as you can modify the size of the disk wihtout having to back up and restore your data. Dynamic disks also support a number of RAID levels.

    StuartR

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    Re: RAID Arrays

    Thanks again, you have assisted me in making my decision, no to RAID.

    Do you think there is any advantage in installing a SATA disk to make complete images of my drives. Instead of using a USB drive or spanning (which I cannot get to work correctly) across DVD's.

    I appreciate your advice.

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    Re: RAID Arrays

    I use additional hard drives to make image backups of all my partitions, but I don't think it is a good idea to leave the disk with the image in the PC. This leaves 2 alternatives.

    Use an external hard drive.
    Backup across the network to a disk in another PC.

    I tend to use the second of these options, but other loungers use external disks.

    StuartR

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    Re: RAID Arrays

    It sounds like you are thinking about SATA to speed the backups up... to which stuart replied: "Use an external hard drive." I just wanted to point out that you can also use external SATA drives if you wanted to - however I don't know the speed differences off the top of my head or if you would actually notice a difference in practice. I'm sure someone here could answer that for you though.
    <img src=/w3timages/blueline.gif width=33% height=2>
    <big>John</big>

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    Re: RAID Arrays

    If you are using a USB external disk drive then USB is more likely the limiting factor for speed than the device. The SATA drives most frequently supplied in new PCs do not have a faster rotational speed than EIDE. Not do they have a larger onboard cache. Nor do they have a faster average seek time. If there is a speed difference it is from the channel architecture.

    Joe
    Joe

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    Re: RAID Arrays

    For what it is worth - You are correct <img src=/S/thumbup.gif border=0 alt=thumbup width=15 height=15>

    Approximately 9 months ago I was working two EXACTLY identical systems with ONE exception. System 1 had 2 Maxtor 200 GB drives and System 2 had 2 150GB SATA Drives. The OS image was blown on both systems using Norton Ghost 10.0.

    Several larege images were then transfered from system's "C" drive to "D" drive and "timed". For sustained disk activity, the SATA out performed IDE. Sorry, can not remember exact times and file sizes - this was not intended as a formal test. Just informal observations as 2 systems were being setup.

    Since then, I had been told the two systems (performing similar functions in same area) were performing at about the same level - with the exception that large file transfers over SATA were faster than IDE.

    Note:External SATA Drives transfer rates are limited by the External plug-in method. USB 2.0 or Firewire.
    Scott

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    Re: RAID Arrays

    Following what Stuart said, I've used both network drives on the LAN and currently two alternating external USB drives for backup images, using TrueImage. To me, the important thing is to have my backups in a device outside the box, in case there is a major disaster that fries the whole computer. The "nice" thing about using external USB drives is that they can be easily shutdown and unplugged if warranted. Given the speed of current imaging programs, I don't know that SATA vs. USB should be a concern to you - they'll both be pretty <img src=/w3timages/censored.gif alt=censored border=0> fast!

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    Re: RAID Arrays

    Al,

    Out of couriosity - which NAS Drives do you use on oyur router/network ?
    Scott

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