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Thread: why is raid-5 not recommended for installations with more than 100 accounts?

  1. #1
    cedbl is offline Senior Member
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    Question why is raid-5 not recommended for installations with more than 100 accounts?

    After testing zimbra 3.1.4
    I had decided to pass to zimbra OSS
    Now in zimbra 4 Administrator's guide I find the note in my title

    I have 380 accounts, my server has 4 hard-disk in raid5 (hardware)
    This is the df-h output
    Filesystem Size Used Avail Use% Mounted on
    /dev/sda3 201G 2.3G 199G 2% /
    tmpfs 506M 0 506M 0% /dev/shm
    /dev/sda1 102M 39M 64M 38% /boot
    /dev/shm 150M 0 150M 0% /opt/zimbra/amavisd-new-2.3.3/tmp

    /dev/shm 150M 24M 127M 16% /opt/zimbra/amavisd-new-2.4.1/tmp

    Can you help me in understanding what's the reason for not recommending raid5?
    If i use only pop3 for the most part of my account and webaccess only for my special accounts can i hope to reduce the impact in the using of the resources?
    Th

  2. #2
    Klug's Avatar
    Klug is offline Moderator
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    Default Speed...

    Hello, welcome to the forum.

    RAID 5 write is slower than RAID 0+1.

    Check this document for additionnal information : http://www.zimbra.com/pdf/Zimbra%20A...20Overview.pdf

  3. #3
    Chris_H is offline Intermediate Member
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    Quote Originally Posted by cedbl
    After testing zimbra 3.1.4
    I had decided to pass to zimbra OSS
    Now in zimbra 4 Administrator's guide I find the note in my title

    I have 380 accounts, my server has 4 hard-disk in raid5 (hardware)
    This is the df-h output
    Filesystem Size Used Avail Use% Mounted on
    /dev/sda3 201G 2.3G 199G 2% /
    tmpfs 506M 0 506M 0% /dev/shm
    /dev/sda1 102M 39M 64M 38% /boot
    /dev/shm 150M 0 150M 0% /opt/zimbra/amavisd-new-2.3.3/tmp

    /dev/shm 150M 24M 127M 16% /opt/zimbra/amavisd-new-2.4.1/tmp

    Can you help me in understanding what's the reason for not recommending raid5?
    If i use only pop3 for the most part of my account and webaccess only for my special accounts can i hope to reduce the impact in the using of the resources?
    Th
    RAID5 is great for optimizing usable space (fewer spindles lost do redundancy needs), but it has several drawbacks that make it less than desireable for a system that needs to have consistent performance characteristics. Writes to RAID5 volumes are slower than RAID1 or 1+0 due to parity calculation, and in addition a RAID5 volume running degraded (e.g. one disk failed) can be dismally slow. Rebuilds of RAID5 volumes are performance-intrusive as well.

    In short, if you don't require the additional capacity provided by RAID5 vs. RAID1 or 1+0, go with 1+0 and you'll get better and more consistent performance.

    Cheers,

    -chris

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    andreychek is offline Special Member & Volunteer
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    Quote Originally Posted by Chris_H
    RAID5 is great for optimizing usable space (fewer spindles lost do redundancy needs), but it has several drawbacks that make it less than desireable for a system that needs to have consistent performance characteristics.
    Yeah... to summarize this using one of my favorite quotes, "RAID 5 is about the slowest way to write to a disk without using a pencil".
    -Eric

  5. #5
    cedbl is offline Senior Member
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    Red face Thanks

    Ok thank-you
    I have to start with raid5 because i have not other possibilities
    At the moment i can't reduce disk-space with raid1 and i have not an other server.
    I was afraid to exceed some hardware limits or to fall in some difficult situation in the case of crash or in restoring full backup
    If "only" performances are concerned i will wait

  6. #6
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    Default :(

    I have 496 accounts in my Zimbra 3.1.4 with RAID5, so I couldn't migrate to version 4.0.4

  7. #7
    inigoml's Avatar
    inigoml is offline Project Contributor
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    Hi Cedbl.

    With that low usage of resources, you should have no problem using RAID5 hardware.
    RAID5 performance impact has been maginified. Current RAID5/6 hardware implementations should have no problem with your config. It's true that RAID5 writing performance is lower than RAID10, but when we talk of only a few hundred of user accounts and most of then are POP3 based, it's not relevant.
    Of course, when you reach a high number of users you will suffer, but not at this moment.
    I've run Exchange 2000 with old RAID5 controllers with 36GB SCSI drives, with up to 1GB user space storage and no problem at all... and we are talking about standard previous century hardware (Dual 550 Xeon, 1 GB, Dell Poweredge 6300.

    Quote Originally Posted by cedbl View Post
    After testing zimbra 3.1.4
    If i use only pop3 for the most part of my account and webaccess only for my special accounts can i hope to reduce the impact in the using of the resources?
    Th

  8. #8
    cmdit is offline New Member
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    Default 300 users using webmail

    Would a RAID5 system be impacted more with people using the webmail client rather than POP3?

    Cheers...

  9. #9
    inigoml's Avatar
    inigoml is offline Project Contributor
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    Yes, of course.
    POP3 users download mail into their mailbox, and usually this email is deleted from server. So, there is no charge in your server and performance will not be affected. However, when accessing via IMAP4 and/or webmail, emails are stored in server and each time you open and email or search, server has to open its database storage. So server load is higher and file system access is constant.

    Quote Originally Posted by cmdit View Post
    Would a RAID5 system be impacted more with people using the webmail client rather than POP3?

    Cheers...

  10. #10
    kollross is offline Senior Member
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    Default follow up

    I see that raid5 is now a no no, but i was wondering if something physically changed in 4.x that would make raid5 not usable. I have 1200+ account system running zimbra 3.1 something running on raid5. This system actually has been running zimbra since M1 with out a huge amount of performance issues. Slighty slow but not a huge deal.

    I saw a previous statement about how he was going to upgrade to 4 but couldn't. Is piece of code that actually restricts this now or is he going by what other people had said. If there is no physical code is there something in 4.X that is going to completely hose my performance vs that of 3.1.x or if 3.1.x is running ok 4.0.4 shouldn't be that much of a difference

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