FDB new features: fill factor

Using FoundationDB
3

So much detailed explanations! Thanks very much! I read it through and still have several questions here, could you please help on them:

  1. when doing update operation in FDB, how is the process? like the value will be updated in-place or not? whether the old value will not be deleted and just marked it as invalid, and then FDB will write the new value in a different node?

2)Here below is my previous test result (storage engine: Redwood, FDB release version: 6.2 no-use-fillfactor ):
using du -BG /opt/data/ we can get the file size information below:
31 /opt/data/fdb-6.2/data/4519
30 /opt/data/fdb-6.2/data/4505
30 /opt/data/fdb-6.2/data/4521
30 /opt/data/fdb-6.2/data/4502
30 /opt/data/fdb-6.2/data/4525
30 /opt/data/fdb-6.2/data/4509
30 /opt/data/fdb-6.2/data/4516
30 /opt/data/fdb-6.2/data/4503
30 /opt/data/fdb-6.2/data/4523
30 /opt/data/fdb-6.2/data/4530
30 /opt/data/fdb-6.2/data/4512
31 /opt/data/fdb-6.2/data/4526
30 /opt/data/fdb-6.2/data/4507
30 /opt/data/fdb-6.2/data/4511
30 /opt/data/fdb-6.2/data/4510
30 /opt/data/fdb-6.2/data/4524
30 /opt/data/fdb-6.2/data/4528
31 /opt/data/fdb-6.2/data/4517
30 /opt/data/fdb-6.2/data/4508
30 /opt/data/fdb-6.2/data/4504
30 /opt/data/fdb-6.2/data/4518
30 /opt/data/fdb-6.2/data/4515
30 /opt/data/fdb-6.2/data/4527
30 /opt/data/fdb-6.2/data/4514
2 /opt/data/fdb-6.2/data/4501
30 /opt/data/fdb-6.2/data/4513
30 /opt/data/fdb-6.2/data/4506
30 /opt/data/fdb-6.2/data/4529
30 /opt/data/fdb-6.2/data/4520
30 /opt/data/fdb-6.2/data/4522
1 /opt/data/fdb-6.2/data/4500
863 /opt/data/fdb-6.2/data

there are 29 storage servers, the saved db size seems to be the same: 30G or 31G, those strong blob 1 is and 2 is not storage server, they are stateless and log server, all the fdb server are the same workstation.
for the test, only about 600G (total recordcount=2000000000, every records is 300 Bytes), but the total final dbset is up to 863GB (please see the last strong blob line ).
my question:
load 600G data, File System du detects 863G, so the gap of 863-600=263G is coming from indexes or something others?
is there any way to check the index size?

Thanks,