Provided by: trafficserver_9.1.3+ds-1_amd64 bug


       volume.config - Traffic Server cache volume configuration file

       The  volume.config  file  enables  you  to  manage  your  cache space more efficiently and
       restrict disk usage by creating cache volumes of  different  sizes.  By  distributing  the
       cache  across  multiple volumes, you can help decrease single-lock pressure when there are
       not many hard drives present. You can further configure these volumes to store  data  from
       certain origin servers and/or domains in the hosting.config file.


       For each volume you want to create, enter a line with the following format:

          volume=volume_number  scheme=protocol_type  size=volume_size

       where  volume_number  is a number between 1 and 255 (the maximum number of volumes is 255)
       and protocol_type is http. Traffic Server supports http for HTTP volume types; volume_size
       is  the  amount  of  cache  space  allocated  to  the  volume.  This value can be either a
       percentage of the total cache space or an absolute value. The absolute  value  must  be  a
       multiple of 128 MB, where 128 MB is the smallest value.  If you specify a percentage, then
       the size is rounded down to the closest multiple of 128 MB.

       Each volume is striped across several disks to achieve parallel I/O. For example: if there
       are  four  disks, then a 1-GB volume will have 256 MB on each disk (assuming each disk has
       enough free space available). If you do not allocate all the disk space in the cache, then
       the  extra disk space is not used. You can use the extra space later to create new volumes
       without deleting and clearing the existing volumes.

          Changing this file to add, remove or modify volumes effectively invalidates the cache.

   Optional ramcache setting
       You can also add an option ramcache=true/false to the volume configuration line.  True  is
       the  default  setting  and  so  not  needed unless you want to explicitly set it.  Setting
       ramcache=false will disable the ramcache that normally sits in front of  a  volume.   This
       may  be  desirable  if you are using something like ramdisks, to avoid wasting RAM and cpu
       time on double caching objects.


       In the following sample configuration 2 spans /dev/disk1 and  /dev/disk2  are  defined  in
       storage.config,  where  span  /dev/disk2  is assigned to volume 3 exclusively (volume 3 is
       forced to an "exclusive" span /dev/disk2).  In volume.config there are 3 volumes  defined,
       where volume 1 and volume 2 occupy span /dev/disk1 taking each 50% of its space and volume
       3 takes 100% of span /dev/disk2 exclusively.


          /dev/disk2 volume=3 # <- exclusive span


          volume=1 scheme=http size=50%
          volume=2 scheme=http size=50%
          volume=3 scheme=http size=512 # <- volume forced to a specific exclusive span

       It is important to note that when  percentages  are  used  to  specify  volume  sizes  and
       "exclusive"  spans  are  assigned (forced) to a particular volume (in this case volume 3),
       the "exclusive" spans (in this case /dev/disk2) are excluded from the  total  cache  space
       when the "non-forced" volumes sizes are calculated (in this case volume 1 and volume 2).


       The  following  example  partitions  the  cache across 5 volumes to decreasing single-lock
       pressure for a machine with few drives. The last volume being an example of one that might
       be composed of purely ramdisks so that the ramcache has been disabled.:

          volume=1 scheme=http size=20%
          volume=2 scheme=http size=20%
          volume=3 scheme=http size=20%
          volume=4 scheme=http size=20%
          volume=5 scheme=http size=20% ramcache=false