PDA

View Full Version : [ubuntu] External Raid Enclosure slow write



Frankincense93
August 6th, 2012, 01:06 PM
Hi guys,

I noticed that when trying to backup my home PCs to my server's external RAID enclosure, it will take long than a day to even do 100GB which is stupid. I have just tried to test the hdd speeds using hdparm and dd;

The main OS HDD:

Read:
sudo hdparm -Tt /dev/sda

/dev/sda:
Timing cached reads: 1220 MB in 2.00 seconds = 609.84 MB/sec
Timing buffered disk reads: 274 MB in 3.01 seconds = 91.00 MB/sec

Write:
dd if=/dev/zero of=/tmp/output bs=8k count=10k; rm -f /tmp/output10240+0 records in
10240+0 records out
83886080 bytes (84 MB) copied, 0.485983 s, 173 MB/s


External RAID enclosure:

Read:
sudo hdparm -Tt /dev/sdb

/dev/sdb:
Timing cached reads: 1250 MB in 2.00 seconds = 625.12 MB/sec
Timing buffered disk reads: 408 MB in 3.00 seconds = 135.84 MB/sec


Write:
dd if=/dev/zero of=/media/RAID/output bs=8k count=10k; rm -f /media/RAID/output
10240+0 records in
10240+0 records out
83886080 bytes (84 MB) copied, 5.28205 s, 15.9 MB/s



Currently I have two 1TB Barracuda SpinPoint SATA 3Gb/s 7200RPM's in RAID 1 in the enclosure. & the Raid enclosure is a Sharkoon 5 bay RAID enclosure.



Any ideas?
Cheers,
Jack

Cheesemill
August 6th, 2012, 01:32 PM
How is the enclosure connected to your machine?

Frankincense93
August 6th, 2012, 02:32 PM
It is over eSata at the moment, but It can be USB aswell.

rubylaser
August 6th, 2012, 03:06 PM
Just with some brief Googling, it appears that your enclosure like most inexpensive RAID enclosures is processor limited. There are a number of examples with users mentioning quick initial speeds and then seeing transfers slow down to 3 MB/s or slower over larger file transfers.

If you can (and are willing), I'd suggest you run the disks in JBOD mode and use them in a software RAID1. That would remove the hardware dependence and should make your sustained transfers much faster.

Frankincense93
August 6th, 2012, 03:37 PM
Ok, well I hope that my mobo supports port multiplying then!

Damn, now I need to setup my RAID again :( , any good links for creating a software RAID?

rubylaser
August 6th, 2012, 04:17 PM
Sure, if you want, you can try my tutorials :) Most are for RAID5/6, but you can substitute the raid level with 1 for RAID1 very easily.

http://zackreed.me/articles/38-software-raid-5-in-debian-with-mdadm

rubylaser
August 6th, 2012, 04:21 PM
Before you do that I would verify that both disks are passing SMART tests. There are no parity calculations in RAID1, so even with an inexpensive RAID enclosure, I would have expected RAID1 to be faster than you're reporting.

But, if you want to go the software route, you can try my tutorials :) Most are for RAID5/6, but you can substitute the raid level with raid1 very easily.

http://zackreed.me/articles/38-software-raid-5-in-debian-with-mdadm