Re: Large Ramdisk creation causes crashes

From: Brandon Ooi (tech_at_hotornot.com)
Date: 10/26/05

  • Next message: William Hooper: "Re: the proper way to 'yum update' a new 'everything' install of FC4?" 
    Date: Wed, 26 Oct 2005 12:13:56 -0700
To: For users of Fedora Core releases <fedora-list@redhat.com>

    Hi Matt,

    I read your I believe it to be a ramdisk limitation because making a
    larger ramdisk, in the exact same manner, gives me a weird error about
    the file system not existing. It's possible that this is a 32bit kernel
    problem that you don't see in x86_64. However, I've experimented with
    x86_64 version of FC3 and we've had trouble with stability in high load
    (random crashes).

    Here is an example of the trial.

    creating a 512+MB ramdisk fails but the 512MB ramdisk suceeds.

    [root@hot52 mnt]# mke2fs -vm0 /dev/ram0 530000
    mke2fs 1.37 (21-Mar-2005)
    Filesystem label=
    OS type: Linux
    Block size=4096 (log=2)
    Fragment size=4096 (log=2)
    66400 inodes, 132500 blocks
    0 blocks (0.00%) reserved for the super user
    First data block=0
    Maximum filesystem blocks=138412032
    5 block groups
    32768 blocks per group, 32768 fragments per group
    13280 inodes per group
    Superblock backups stored on blocks:
            32768, 98304

    Writing inode tables: done
    Writing superblocks and filesystem accounting information: done

    This filesystem will be automatically checked every 22 mounts or
    180 days, whichever comes first. Use tune2fs -c or -i to override.
    [root@hot52 mnt]# mount /dev/ram0 r0
    mount: wrong fs type, bad option, bad superblock on /dev/ram0,
           missing codepage or other error
           In some cases useful info is found in syslog - try
           dmesg | tail or so

    [root@hot52 mnt]# mke2fs -vm0 /dev/ram1 524288
    mke2fs 1.37 (21-Mar-2005)
    Filesystem label=
    OS type: Linux
    Block size=1024 (log=0)
    Fragment size=1024 (log=0)
    131072 inodes, 524288 blocks
    0 blocks (0.00%) reserved for the super user
    First data block=1
    Maximum filesystem blocks=67633152
    64 block groups
    8192 blocks per group, 8192 fragments per group
    2048 inodes per group
    Superblock backups stored on blocks:
            8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409

    Writing inode tables: done
    Writing superblocks and filesystem accounting information: done

    This filesystem will be automatically checked every 39 mounts or
    180 days, whichever comes first. Use tune2fs -c or -i to override.
    [root@hot52 mnt]# mkdir r1
    [root@hot52 mnt]# mount /dev/ram1 r1
    [root@hot52 mnt]# df -h
    Filesystem Size Used Avail Use% Mounted on
    /dev/sda5 4.0G 1.3G 2.8G 31% /
    /dev/sda1 99M 8.8M 85M 10% /boot
    /dev/shm 1.5G 0 1.5G 0% /dev/shm
    /dev/sda6 63G 2.4G 61G 4% /hot
    /dev/sda2 4.0G 35M 3.9G 1% /tmp
    /dev/ram1 496M 2.3M 494M 1% /mnt/r1

    Brandon

    Matt Roth wrote:

    >
    > Brandon,
    >
    > I can't specifically comment on your problem because I haven't
    > encountered it, but one thing in your description seemed strange. I
    > don't believe there is a kernel limit on the size of the RAM disk. We
    > are running the x86_64 version of FC3 on a machine with 20GB of RAM
    > with a 16GB RAM disk to overcome some I/O bottlenecks we encountered
    > when digitally recording large numbers of VoIP calls.
    >
    > The details of our setup can be found here:
    >
    > http://lists.digium.com/pipermail/asterisk-users/2005-October/127919.html
    >
    > Just search for "RAM Disk Setup" because the document is mainly about
    > NFS optimization and Asterisk.
    >
    > You seem to be experiencing some strange problems and it's my advice
    > that you start at the beginning (the RAM disk limitation) and work
    > your way forward.
    >
    > I hope this is helpful to you,
    >
    > Matthew Roth
    > InterMedia Marketing Solutions
    > Software Engineer and Systems Developer
    > 

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