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  1. #1
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    Cool FSCK on SCSI RAID1/5 array

    Hello,

    I have never used RAID5 SCSI because I was affraid of FSCK's taking lots of time.

    However, last time, I needed a FSCK that took almost 1 hour for a RAID1 of 2x 73GB scsi drives. This has make me curious whether it isn't better to go for RAID5 with a hotspare or RAID1, since the fsck-time might be almost the same.. 1 hour for a fsck is alot anyway

    For a new server, I'm looking into one of the two configs:
    RAID1:
    2x Hitachi 146GB U320 SCSI 10Krpm 80Pin 527.25 = 1,054.50
    RAID 5 (1HD HOTSPARE!)
    4x Hitachi 073GB U320 SCSI 10Krpm 80Pin 240.68 = 962.72
    Anyone who has experience with fsck on raid 5 arrays? Any input is accepted

    Thank you!

  2. #2
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    I forgot to add that RAID5 is actually cheaper (see pricing), even cheaper than 4x73drives (one configured as a hotspare)

    Thanks!

  3. #3
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    Reading from a RAID5 array is probably about the same performance-wise as reading from a RAID1 array. Where you take a small performance hit with a RAID5 array is in writes. fsck spends most of its time reading, so you shouldn't see much of a difference. You can also imagine that for web-hosting applications, the ratio of large reads to writes heavily favors the reads (small writes, such as to log files, or a mail spool on a lightly loaded mail server) should take advantage of the buffer, and so shouldn't take a hit).

    Do keep in mind that you'll need a hardware RAID controller for RAID5. Software RAID works quite well for RAID1, but the checksum computation and other overhead of RAID5 really should be done by hardware.
    Last edited by bqinternet; 05-22-2004 at 04:53 PM.
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  4. #4
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    Oh, and on FreeBSD, we have background fsck, so the server boots up in about a minute, with most of that time being for a memory check.

    You could say that FreeBSD is a 1 minute fsck
    Scott Burns, President
    BQ Internet Corporation
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  5. #5
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    I noticed a helpful remark regarding FreeBSD, and thought I'd add to that. If you run Linux and are concerned about fsck times, you should strongly consider converting your filesystems to ext3. It's basically the same as ext2, but with journalling support added on. It works well and is a huge time saver for big disks.
    Jeff at Innovative Network Concepts / 212-981-0607 x8579 / AIM: jeffsw6
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  6. #6
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    Originally posted by bqinternet
    Oh, and on FreeBSD, we have background fsck, so the server boots up in about a minute, with most of that time being for a memory check.

    You could say that FreeBSD is a 1 minute fsck
    I'm not sure, but Linux does have a background fsck, allthough it doesn't fix everything.

    Originally posted by jsw6
    I noticed a helpful remark regarding FreeBSD, and thought I'd add to that. If you run Linux and are concerned about fsck times, you should strongly consider converting your filesystems to ext3. It's basically the same as ext2, but with journalling support added on. It works well and is a huge time saver for big disks.
    I'm using ext3, so I guess raid5 doesn't increase fsck time too much

    Thank you all for your helpfull input

  7. #7
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    Sounds to me like your init scripts may be performing an ext2 style fsck on your ext3 filesystems, which is not necessary.
    Jeff at Innovative Network Concepts / 212-981-0607 x8579 / AIM: jeffsw6
    Expert IP network consultation and operation at affordable rates
    95th Percentile Explained Rate-Limiting on Cisco IOS switches

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