Convert key value pair into hash

I have a field p1 with the value as partition=root,size=23.28GB,free=15.76GB

p1 : partition=root,size=23.28GB,free=15.76GB

I want to store this in an array field and the values in a hash, like below.

[partition][root] : {
                     size = 23.28GB,

Please help me to achieve this.

If you want the field name to be a variable you will have to use a ruby filter.

    dissect { mapping => { "p1" => "partition=%{[@metadata][partitionName]},size=%{[@metadata][size]},free=%{[@metadata][free]}" } }
    ruby {
        code => '
            h = { "size" => event.get("[@metadata][size]"), "free" => event.get("[@metadata][free]") }
            name = event.get("[@metadata][partitionName]")
            event.set("[partition][#{name}]", h)

Error handling is left as an exercise for the reader.

If you want to convert those GB to actual numbers then check out the bytes filter.