Very slow volume expand on Synology ds2413+

I've posted this elsewhere on the internet aswell, and will obviously reply in both places if a proper solution is found.

I am attempting to expand SHR volumne (2x4TB, 1x2TB) with additional 4TB drive on a ds2413+. The 4TB drives are WD Red, the 2TB are WD Green.

Expansion has completed 12% in around 4 hours and 30 minutes. Extrapolating this tells me it will take another 36 hours. After that, I need to migrate 3 other old 2TB drives to this new NAS (First move data, then expand volume again with these 3 additional drives).

It seems that the NAS will not be deployable for close to a week.

Is there any way to speed up the process ?

Some facts/info:

• Device is Synology ds2413+

• DSM 5.0, update 1

• The device can be left alone while expanding, if needed.

• CPU is hovering at around 14%

• RAM is 5% (of 2GB)

• /proc/sys/dev/raid/speed_limit_max states 200000

• /proc/sys/dev/raid/speed_limit_min states 10000

• Noone has been using the device while expanding so far.

• /proc/mdstat: (Note the very slow speed)

And here is the output of cat /proc/mdstat:

cat /proc/mdstat

Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]

md3 : active raid5 sde6[2] sda6[1] sdc6[0]

  1953494784 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/3] [UUU]

resync=DELAYED
md2 : active raid5 sde5[3] sda5[0] sdc5[2] sdb5[1]
  3897559296 blocks super 1.2 level 5, 64k chunk, algorithm 2 [4/4] [UUUU]

  [=====>...............]  reshape = 26.9% (525738624/1948779648) finish=1007.8min speed=23531K/sec
md1 : active raid1 sde2[3] sda2[0] sdb2[1] sdc2[2]
  2097088 blocks [12/4] [UUUU________]
md0 : active raid1 sde1[3] sda1[0] sdb1[1] sdc1[2]
  2490176 blocks [12/4] [UUUU________]

The results from my immediate googling are several years old, and for an older version of DSM. The only thing I saw was raising speed_limit_max and speed_limit_min, but there was no mention of whether it could be done during the expansion process.

What can I do to increase the speed of this expansion?

Would there be anything wrong with simply raising the speed_limit_max and speed_limit_min values ?

Are other details needed to assist ?

Any help would be greatly appreciated.

EDIT: Adding this in case anyone finds this using google and was wondering how long expansion actually takes.

I didn't end up tweaking anything for the expansion process.

Initial setup was 2x4TB, 1x2TB in SHR-1.

First expand was with an additional 1x4TB drive. There was ~3TB of data on the volume. This took ~35h:30m.

Second expand was with an additional 3x2TB drives. There was ~6,5TB og data on the volume. This took ~18h:15m.

All 4TB drives were WD Red, and 2TB drives WD Green.

And just for the record: You can't move form SHR-1 to SHR-2 after the volume has been created. You need to choose that during setup (Which I'd like to have done in retrospect. Due to the potential long rebuildtime in case of a drive failure and subsequent risk of an additional failure during the rebuild process)