Do I need ZIL zfs protection?

Question

ZFS

Actually what do I want to do? Create not expensive, but productive storage (data storage) available via iscsi for esxi.
My suggestions on how to do it better:
1. Use hardware edition 10 Adaptec ASR6805E (available) It doesn’t have batteries and it seems like you can’t buy it in addition, if I’m wrong, I’ll be glad if anyone knows which one can be installed. Therefore, the cache on it will be disabled.
2. Use zfs on partition
3. Use 8 gigs of memory for L1 cache
4. Use 30 gig MLC SSD for L2 cache
5. Use SSD SLC 30 gigs for ZIL. Here is just the question, the loss of this partition will result in the loss of data written to the partition? And will the problems of writing to it be displayed somewhere in the logs? Considering that the disk can quickly fail, this is probably a bottleneck and an important place.
Maybe I'm doing something wrong? Maybe there are some recommendations for a more optimal storage building. Or is it easier and cheaper to buy a raid with a battery and ssd cache instead of ssd disks (as far as I know, the price starts from 60t.r.)?
The storage will have 4 x 2TB WD Black RE drives
Thanks in advance for your help

Answer 1

Yes, you are right, 2 mirrors were created and a record on both.
Everything was measured by the gstat utility by measuring through zabbix once every 5 seconds
the random read load was created by running defragmentation on a virtual machine running on a partition connected via iSCSI ESXI 5.5
And at that moment the measurement was carried out.
And the write speed itself was measured by copying the file from the network balls to the virtual machine.
Server parameters
FreeNAS-9.3-STABLE-201509220011
Intel(R) Xeon(R) CPU X3440 @ 2.53GHz
DDR3 16Gb memory
Can you try to deploy raid 10 on a separate controller without caching, and partition and caching already using ZFS?