Slow write speeds

[kewtips]

Hi all,

 

I am struggling with write speeds on my N54L running UnRAID basic 5.05 (so no cache drive). Speeds seem to be stuck at 1-2MB/s,  I attach the system log.  I have also performed SMART checks the disks and I have cycled the network switch.  I have also started in safe mode but the performance persists.

 

I have searched the forums and tried the tips but no luck so far.  Any thoughts gratefully received.

 

Thank you.

syslog.txt

[superloopy]

Is this a newly built system or have your drive speeds just recently become poor? Have you ever seen decent speeds (around 30MB/s if using parity) on this system?

 

[kewtips]

Hi,

 

This is a new build that has been up and running for about 4 weeks.  I am pretty certain that the write speeds have been consistently low or at least, since the parity drive was installed 2 weeks ago.  Both parity and drive 1 are new 2TB WD Reds.  There is a legacy 500GB drive as drive 2 which came out of an old time machine which is scarcely used.  The parity check speed was estimated at around 80MB/s-I will get the actual speed when I return home this evening.

 

J

 

[superloopy]

I've got a couple of N54L servers and write speeds are between 25-35MB/s with parity disc operating. Parity checks run at 88-140ish. Have you 'modded' your system at all? Your drives are all on the mobo sata ports .... there's no add in card at all?

 

Looking at your syslog (i'm no expert but am sure someone WILL take a good look soon) i'd say your problem is with ata4, which may well be your 500GB drive and seems to be handling data at UDMA/100 and not sata speeds and as unRAID will only transfer data at the speed of your slowest drive, my understanding only,  then you're being crippled by this drive. Any way you can remove it and reset your config if, as you say, its hardly used? Move any data to the 2TB drive. I'm assuming it's sata1 drive, yes?

 

Just my thoughts ... an 'expert' will no doubt be around the next corner

 

[kewtips]

Hi,

 

Back at home now. 

 

The system is not modded at all except I did install the BIOS to unlock the full SATA speeds for the top bay-this is not used yet.

 

ATA4 is the 250GB disk that was provided with the server.  It is not part of the array. 

 

I have replaced the cable between the server and my network.-the speed is still 1-2MB/s.

 

A couple of thoughts. 

[*]I am using a very old USB drive-but the operations take place in RAM right?

[*]I have 2 RAM sticks: 1MB and 4MB and these are not matched

Are either of these likely candidates?

 

Thank you

[garycase]

... unRAID will only transfer data at the speed of your slowest drive...

 

FYI, that's not true UNLESS you happen to be writing to that drive (and then it will be even slower, since there are multiple disk I/O's for each write to preserver fault-tolerance.

 

 

I am using a very old USB drive-but the operations take place in RAM right?

I have 2 RAM sticks: 1MB and 4MB and these are not matched

 

Are either of these likely candidates?

 

No, neither of those should be impacting the write speeds to the disk.

 

 

Question:  Is this slow transfer speeds ONLY for writes?  i.e. do reads occur at normal speeds?

 

Also, have you tried changing the Ethernet cables?  [ALL of them that are involved in any transfers to/from the UnRAID server -- from server to UPS; from UPS to switch;  from switch to router;  from router to PC;  etc.]

 

 

[superloopy]

Thanks for the heads-up Gary .... i'm sure i've read on here that slowest disk = write speed but always open to new info!

 

 

[garycase]

What you may be thinking of is parity check speeds.  At any moment in time, the parity check speed is limited by the slowest disk that's still involved in the check ... e.g. if you had a VERY slow 250GB drive in your system, then the first 250GB of a parity check would be limited by it -- after the check got past the 250GB point, that drive would no longer be involved, so would no longer be a limiting factor.

 

[kewtips]

I have just done some tests. 

Read speed is 57.1 MB/s

Write speed 1.3 MB/s

[garycase]

I have just done some tests. 

Read speed is 57.1 MB/s

Write speed 1.3 MB/s

 

First thing I'd do is (as I suggested above) replace ALL of the Ethernet cables involved in transfers between your PC and the server ==> you said earlier you replaced the cable "between the server and my network" ... but I assume there are other cables involved in the transfers as well.  Also, if you haven't already done so, try a different switch/router port.

 

[JonathanM]

I have just done some tests. 

Read speed is 57.1 MB/s

Write speed 1.3 MB/s

Assuming that all the data on this machine is backed up elsewhere, I'd temporarily set a new config WITHOUT the parity drive assigned, and redo your tests.

[kewtips]

Thanks all.  I have just replaced the cables and the switch.  This makes no difference to the write speed  All the cables are 5e.

 

I will try disabling parity next.

[kewtips]

Okay.  With parity disabled, write speed becomes 68.6 MB /s.  Read 67.5 MB /s.  Ok looks like I managed to test an internal drive.  See below.

[JonathanM]

Okay.  With parity disabled, write speed becomes 68.6 MB /s.  Read 67.5 MB /s

Smart report on parity drive? Did you preclear the drives before you installed them to check for infant mortality?

[kewtips]

Hi,

 

yes all the drives were pre-cleared including the parity drive (although I understand that this is not strictly necessary).

 

I attach the smart report for the parity drive:

 

Many thanks for your help.

 

NOTE: updated with recent SMART scan.

 

smart_SDA_02.txt

[kewtips]

OK scratch the previous post.  Write speeds with Parity off are 1.3MB/s.  I think I managed to test one of the internal drives previously.

 

I will order some new cables and see if that makes a difference.  Any other ideas gratefully received.

[garycase]

What is the SOURCE for your writes?

 

What kind of speeds do you get if you write from the same source to another PC on your network (NOT the UnRAID server) ??

 

[kewtips]

I am writing from my main PC.  It is a dual boot Windows/OSX machine.

 

Running tests from windows:

disk 1 (WD red 2TB) 9MB/s write, 99MB/s read

disk 2 (old seagate driver 500GB) 24MB/s write, 99MB/s read

 

Thanks, J

[kewtips]

OK

Using MC to do a 1GB internal transfer from:

disk 1 to disk 2-achieves 40-60 MB/s

from disk 2 to disk 1 6MB/s

It definitely looks like a write problem with the WD red but weird this does not appear in the SMART tests.

 

Can anyone recommend any other diagnostics?

 

 

 

[garycase]

I'd swap out disk1 with another 2TB drive.    From your results, this may resolve the issue ... then you can simply get the drive replaced via RMA and use the replacement as either another data drive or a backup.

 

[superloopy]

Could this not be the backplane? It's an HP microserver, yes? Is it possible to swap the two WD drives and see if the low write speed then affects disk2? Normally you'd do this with the sata cables themselves and see if the problem moves across but the HP is a different beast.

 

Gary ... is it possible to move drives around without affecting current config .... it's 5.0.5 as i understand so should be ok?

 

[garycase]

True -- hadn't thought about the HP backplane.    Just to confirm that's not the issue, move the drive to a different position.  As noted above, with v5 you can freely move the disks to different ports and UnRAID will still recognize the current configuration.

 

[kewtips]

Thanks everyone.  i had already tried swapping the disks between slots. 

 

I am currently pre-clearing the Parity disk (3 cycles  ) and will see if that drive performs better.  If it does, i will RMA the slower disk and use the replacement as parity (the data is backed up elsewhere).

 

J

 

Thanks again for the ideas and help.

[kewtips]

Ok, the plot thickens.  With MC:

The old parity drive seems fine- internal copies are at around 30MB/s-not stellar but within parameters.

The "faulty" drive copies  at around 10MB/s-  Can I RMA this?

 

More interesting are network results.

Widnows:

old parity: windows read 812Mb/s.  Write 204Mbps (niiiiice!)

faulty drive read 827Mb/s, write 91Mbps (limited by drive speed?)

Max OS X 10.4

old parity read 819 Mb/s, write 84Mb/s

 

I think I have two overlapping problems:

1. A poor drive

2. OSX network write weirdness

 

Any pointers again gratefully received.

 

 

 

[garycase]

Can I RMA this?

 

I would.  I've never seen WD challenge the reason for an RMA.  I'd also do the "Advanced Replacement" RMA ... they'll send you a drive; then you return the old one in the same mailer.  Makes things a lot easier for the swap.

 

Can't help with the OSX issue ... but it's likely protocol related.  Don't have a Mac, so I've never tried AFP and don't know what the settings need to be.  Hopefully someone with a Mac will help with that.