Testing Migration to Wired Tiger from MMAP0 in 2.6 by adding a WT Replica.

Servers:
Data Volume - 1 TB
Servers Amazon C4.2XLarge
8 x CPU
15GB RAM
Disks 2 x 1TB SSD EBS with 4000PIOS in Raid 0 (8000 PIOPS)

No load on source (primary) server
522,771,027 Documents in collection

Data Copying Phase:
Began: 08:15 16th Jan
Finished 18:23 16th Jan

Creation of _id Index (_id is standard OID's)

2015-01-16T18:23:17.006+0000 I - [rsSync] Index Build: 123300/522771027 0%

Currently

2015-01-17T19:09:58.004+0000 I - [rsSync] Index Build: 150625100/522771027 28%

Not only over 24 hours for 28% but observably taking 4 minutes longer per 1%

At 396 minutes for the final 1% Total predicted time is

396/2 * 100 = 330 Hours to build one index.

By comparison - I tested 2.6 on the same hardware and this step took 7hrs 36 minutes.

Is this the case for all WT index creations - is time to build polynomial (and greater than n log n I think) with number of records - Is this just increasing indexes or all indexes. If I had 3 or 4 secondary indexes on this are they built sequentially or in parallel?