I've been waiting to set up Unraid for a while and finally found some time over the last weekend. I have a total of five WD 14TB HC530 drives to transfer data from.

My plan is to start with a 1-drive array:

1. Transfer data over from my other drives one by one (Maintain hardlinks)

2. After data is transferred, add the drive to the array

3. After everything is transferred, add and set up the parity drive.

However, I noticed that the transfer speed is extremely slow when transfering to the share and to the mounted disk, and I'm at a loss as to what could be causing this.

I have my array at /mnt/user/data and my data drive mounted at /mnt/sdb

Test 1: Verify drive read & write speeds on both drives ✅

dd write: 10737418240 bytes (11 GB, 10 GiB) copied, 49.5819 s, 217 MB/s
dd read: 10737418240 bytes (11 GB, 10 GiB) copied, 41.7951 s, 257 MB/s

Test 2: Transfer Test

rsync -aHAXS --progress --stats --human-readable --no-compress data_dir array_disk_dir

From	To	Write Speed
/mnt/sdb	/mnt/user/data	25MB/s
/mnt/sdb	/mnt/disk1/data	140MB/s

Would appreciate some pointers so I can dig into this

Issue 2: Dirty Memory Limits?

A second issue I noticed is that when my system's dirty memory reaches ~3GB (10% of my total memory on the system), it stalls either the read or the write down to just 2-3MB/s until it's cleared, which occurs in both test cases.

I tried tuning them, but it didn't affect the ~3GB mark. Either the set the ratio and nothing happens, or I set it by bytes and it doesn't use the dirty memory at all and transfers ~30MB/s, so I'm not sure if there's something I'm overlooking here. It seems like it's reading the data drive to memory first, and then transferring to array - would love any advice on how I can optimize this further too

Edited June 28, 20251 yr by Tohsaka

Are you copying large or small files?

Also post the diags during a transfer.

Turns out it was the sparse flag in my rsync that caused the slowdown. I'm not sure why it was as drastic as 5x slowdown (as well as the dirty memory problem), but removing it solved it.