Re: How's RAID doing?

From: Måns Rullgård (mru_at_inprovide.com)
Date: 06/13/05

  • Next message: Parminder Lehal: "dvd WRITE@LBA=0h" 
    Date: Mon, 13 Jun 2005 01:03:48 +0200

    martingerxt@yahoo.com writes:

    > Tauno, doesn't Linux do RAID 5 as well? Why would I want to do RAID 1
    > instead of 5?

    Linux supports RAID 0, 1, 5, and recently 6 (still experimental). It
    also supports the obsolete RAID 4.

    For RAID 5 you need at least three disks. Two rather large disks are
    usually cheaper than three somewhat smaller disks. If you need huge
    amounts of space, RAID 5 or 6 is the way to go.

    > Also if I do IDE, aren't I limited to 4 disks without a special
    > motherboard, 3 if I have a cd/dvd drive?

    Never use more than one drive per IDE cable, especially if you are
    doing RAID. Only one of them can be active at a time, and doing RAID
    1 using drives on the same cable will halve your writing speed.

    The implication of this is that the builtin controller on most
    motherboards will be good for only two disks. Add a PCI controller if
    you need more.

    Having two CD/DVD drives on the same cable is usually not a problem,
    since they are rarely used anyway. Sharing a cable between a CD/DVD
    and a hard disk is a really bad idea. It will force the disk to use
    the usually lower speed of the CD/DVD.

    > I've heard that IDE/ATA gives much more bang for the buck than SCSI
    > on Linux RAID. I really don't need to do hot swapping.

    I suppose the prices of the drives speak for themselves. The SCSI
    drives do have some advantages, though, such as higher transfer rates,
    and shorter seek times. Which is best depends on your specific
    application. Adding a gigabyte or a half of extra RAM can also do
    wonders with respect to access time to your data, if the access
    pattern is such that it benefits from caching.

    For a new system where SCSI drives are not warranted, I would go for
    SATA. It is somewhat faster than ATA, and I suspect that the price of
    SATA drives will drop below ATA in not too long a time. Most new
    motherboards also come with at least two SATA ports. Finally, the
    thinner SATA cables make for better airflow inside the box, which
    helps keeping the temperature of the disks down. 

    -- 
Måns Rullgård
mru@inprovide.com
  • Next message: Parminder Lehal: "dvd WRITE@LBA=0h"

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