How to properly detect if storage is full?

[cannium]

As I can see, there're several limitations:

• journal area is full
• data area is full
• data area is not full, but cannot allocate new objects larger than "certain" size
• file system is full, which is avoided by pre-allocation

Upper layer application needs this information to determine if a volume is still writable, maybe this could be reported by Usage.

[thesues]

I updated the Usage function in storage.go.

the storage.Usage function now should be thread-safe. you can call it anytime you want.

the output is like this:

{
  "journalcapacity": 10737664,
  "datacapacity": 1063003648,
  "filecounts": 272,
  "datafreebytes": 652605440,
  "journalusagebytes": 7920
}

[cannium]

Thread-safe is nice to have, since it's already handled in upper layer: https://github.com/journeymidnight/seaweedfs/blob/yig2/weed/storage/volume_read_write.go#L92

And what about case 3: data area is not full, but cannot allocate new objects larger than "certain" size?

[thesues]

You are brilliant to notice this corner case. Since the the data is aligned to block size,
I think certain size = min(lump.LUMP_MAX_SIZE, datacapacity - datafreebytes -2)

[cannium]

I think free space could be fragmented.

[thesues]

Done in commit#806dfbba
each allocation or release will update maxSegmentSize to size of freelist's max portion