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Ello everybody, I'm looking for an answer to why, if linux has a built in function that cache disk writes, would I need a cache on my RAID card? Is ...
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  1. #1
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    Linux and HDD cache


    Ello everybody,

    I'm looking for an answer to why, if linux has a built in function that cache disk writes, would I need a cache on my RAID card?

    Is it a "bad" caching feature in some way?

    I have alot of servers, now I'm working on a laboration server to have at home, nothing important on it so I don't need a RAID-card with a bbu for write security or anything like that.

    What I do need is some speed...

    The RAID card that I have left over have no cache at all. The card works perfectly except the performance is really bad. It has to confirm all writes to disk and that takes an awful amount of time.

    I used a SSD-drive for handing the cache and that works alot faster, problem with SSDs is that they can only handle so many R/W before they die.
    I can use a RAM-drive also.
    I can buy a RAID-card with cache.

    But why don't the built in function handle it for me?

    Best regards

    Johan

  2. #2
    Linux Guru Rubberman's Avatar
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    Quote Originally Posted by dexznrl View Post
    Ello everybody,

    I'm looking for an answer to why, if linux has a built in function that cache disk writes, would I need a cache on my RAID card?

    Is it a "bad" caching feature in some way?

    I have alot of servers, now I'm working on a laboration server to have at home, nothing important on it so I don't need a RAID-card with a bbu for write security or anything like that.

    What I do need is some speed...

    The RAID card that I have left over have no cache at all. The card works perfectly except the performance is really bad. It has to confirm all writes to disk and that takes an awful amount of time.

    I used a SSD-drive for handing the cache and that works alot faster, problem with SSDs is that they can only handle so many R/W before they die.
    I can use a RAM-drive also.
    I can buy a RAID-card with cache.

    But why don't the built in function handle it for me?

    Best regards

    Johan
    Have you tried just using the Linux software raid tools? They can take advantage of the system write cache. Also, you might be able to tune the card's mount options in order to better take advantage of such system capabilities. Post the contents of your file /etc/fstab here so we can better advise you about that.
    Sometimes, real fast is almost as good as real time.
    Just remember, Semper Gumbi - always be flexible!

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