[DRBD-user] DRBD on ramdisk

HIROSE, Masaaki hirose31 at t3.rim.or.jp
Thu Aug 18 12:06:52 CEST 2005

Note: "permalinks" may not be as permanent as we would like,
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in "Re: [DRBD-user] DRBD on ramdisk"
   <43021A1B.200 at arx.net>
at Tue, 16 Aug 2005 19:53:47 +0300,
   tchatzi at arx.net wrote:

> >>  Is there a possibility of serious problem on DRBD on /dev/ramX?
> >
> >I don't know. We never really considered such usage.
> >
> >I know that someone one this list used to have his apache session data
> >on a drbd on ram disk, and it seemd to work well for him.
> >  
> >
> That would be me :)
> It does work quite reliably, but I suspect that it won't do what you 
> expect, if I read your post right.
> Something like NFS mounted directories is probably what you need. But 
> you sure are welcome to drbd those...

I want to NFS export DRBD directory. Tomcat is running on each NFS
clients and Tomcat stores serialized session data into NFS mounted
directory and share session data with another Tomcat.

and I want to use memory base device (ramdisk, tmpfs) as backend of
DRBD instead of hard disk.

because of
  - more faster. Tomcat should process many accesses.
  - more troubleless. hard disk is breakable...


I have new trouble... I do stress test, then use% of /dev/drbd become
100% so remove all files and directories but use% is still 100%...

  # df /mnt/drbd
  Filesystem           1K-blocks      Used Available Use% Mounted on
  /dev/drbd1              258768    258756 12 100% /mnt/drbd
  # df -h /mnt/drbd
  Filesystem            Size  Used Avail Use% Mounted on
  /dev/drbd1            253M  253M   12K 100% /mnt/drbd
  # find /mnt/drbd -type f
      (no outpu) 
  # fuser -mv /mnt/drbd/
      (no output)

Is there potential problem in DRBD on ramdisk? I would be very
grateful for any kind of information.

way to setup /dev/drbd1
  boot with ramdisk_size=524288
    on drbd01 {
      device     /dev/drbd1;
      disk       /dev/ram3;
      address    XXX.XXX.XXX.XXX:7789;
      meta-disk  /dev/ram1[1];
  mkfs.xfs -f -s size=1024 -b size=1024 -i size=512,maxpct=0 -d size=268435456 /dev/drbd1

NFS server exports following configuration.
  /mnt/drbd XXX.XXX.XXX.XXX/,no_root_squash,async)

NFS clients mounts following mount option.
  -o rw,soft,intr,rsize=8192,wsize=8192,noac

stress test is following.
  - loop
      fork 3 processes. and each process do following in background
        repeat 1000 times
          cat 0 > 1
          rm -f 1
  - loop
      bonnie++ -s 32 -r 0 -n 20:4096:2048 -x 1

I do stress test on three NFS clients coincidently.

The 'used 100%' problem occurred about 9 hours later.

There is no problem in case of NFS exports /dev/ram3 directry. (stress
testing 24 hours)

HIROSE Masaaki

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