Slow resilvering with mirrored ZIL

[Maxim Bourmistrov]

Hello list@,

I'm in the middle of replacing my old hard drives with new ones on my ZFS NAS.
There are at least two ways to accomplish this. 
I'm however, doing resilvering of new ones.

While doing a resilvering of one of possible four drivers I had 40-60 MB/s resilvering speed.
ZIL is located on a 10G partition on an Intel SLC SSD.
It toke about 24h to resilver about 1.5T.

Then I decided to create a 10G partition on another SSD(OCZ AGILITY 3 , MLC) and created a mirror of ZIL.
Done that, I continued to resilver the second drive out of four and noted significant speed drop of resilvering.
5MB/s as of now.

I understand that doing a ZIL mirror will result in performance penalty, but not that much?!

Box is slightly loaded and I tried to completely shutdown all services and disconnect it from LAN in order to isolate it, without any improvements in speed.


Any ideas?
Am I completely wrong in assuming that ZIL is involved in resilvering process?

P.S.

SSDs:

ada4: <INTEL SSDSA2VP020G2 2CV102M5> ATA-7 SATA 2.x device
ada4: 300.000MB/s transfers (SATA 2.x, UDMA6, PIO 8192bytes)
ada4: Command Queueing enabled
ada4: 19087MB (39091248 512 byte sectors: 16H 63S/T 16383C)
ada4: Previously was known as ad12
ada5 at ahcich5 bus 0 scbus5 target 0 lun 0
ada5: <OCZ-AGILITY3 2.15> ATA-8 SATA 3.x device
ada5: 300.000MB/s transfers (SATA 2.x, UDMA6, PIO 8192bytes)
ada5: Command Queueing enabled
ada5: 57241MB (117231408 512 byte sectors: 16H 63S/T 16383C)
ada5: Previously was known as ad14