Very Very Slow Write Speed


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1 hour ago, whipdancer said:

I'm not asking what a data drive is.  I'm asking what kind of drive are you specifically using for your data drive?

You cross posted this question all over the place - did you read the Seagate thread you posted on? It has an answer for you.

Hi Whipdancer,

I was just wondering if you know the reason for slow speed. You meantioned that other thread has an answer but I don't see anything there . Seems everyone is reporting all good with "Model Family:     Seagate Barracuda Compute and Device Model:     ST8000DM004-2CX188" hard drives. 

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28 minutes ago, johnnie.black said:

New config (Tools -> New config) makes Unraid "forget" current assignments, after doing it you'll need to reassign the disks, but nothing will be deleted on the disks assigned as data drives, if they have data and were formatted by Unraid or UD it will still be there, starting the array after a new config will re-sync parity, i.e. create valid parity, you just need to be careful and don't assign a disk with data to the parity slot.

Johnie, Do you think it could be because of underline 1 SAS connector which is gettign split into 2 SATA Connectors (1 for Parity and 1 for Data Drive) ??

 

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1 hour ago, ManishGupta8 said:

Hi Whipdancer,

I was just wondering if you know the reason for slow speed. You meantioned that other thread has an answer but I don't see anything there . Seems everyone is reporting all good with "Model Family:     Seagate Barracuda Compute and Device Model:     ST8000DM004-2CX188" hard drives. 

The SMR drives use a cache (I think) for small writes that preserve the speed. Once you exhaust that cache you encounter the actual speed at which the drive writes to the disk. My SMR drives (i have 5 of them) all offer average sustained speeds between 30mb/s and 40mb/s. My newest Toshiba 8TB drive offers average sustained speeds between 130mb/s and 215mb/s.

If you use preclear to prep your drives for use in unraid, it reports on average speeds (which is where I got my numbers from).

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41 minutes ago, whipdancer said:

The SMR drives use a cache (I think) for small writes that preserve the speed.

Yes, they have a multi-tier cache, usually comprised of RAM -> Flash -> PMR and only then SMR, what's interesting is that the old Seagate Archive drives were very good at detecting sequential writes, and as long as you were writing large files they kept up with good speeds, for example, this is a server with only 8TB Seagate Archive drives:

 

Turbowrite.png.a970075aba1e0fa8c8c2aff558d38214.png

 

Total transfer size was about 150GB of large files, and speed remained constant, but not all SMR drives can do this, for example I have a few WD 2.5" 1TB SMR drives, and even for sequential transfers with large files they are only fast for the first 50GB or so and then write speed decreases to around 25MB/s, and possibly the newer SMR Seagte Barracuda drives behave similarly, which would still be kind of strange since the Archive drives work so well, but like I mentioned there are other reports of these models being slow.

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5 hours ago, johnnie.black said:

Yes, they have a multi-tier cache, usually comprised of RAM -> Flash -> PMR and only then SMR, what's interesting is that the old Seagate Archive drives were very good at detecting sequential writes, and as long as you were writing large files they kept up with good speeds, for example, this is a server with only 8TB Seagate Archive drives:

 

Turbowrite.png.a970075aba1e0fa8c8c2aff558d38214.png

 

Total transfer size was about 150GB of large files, and speed remained constant, but not all SMR drives can do this, for example I have a few WD 2.5" 1TB SMR drives, and even for sequential transfers with large files they are only fast for the first 50GB or so and then write speed decreases to around 25MB/s, and possibly the newer SMR Seagte Barracuda drives behave similarly, which would still be kind of strange since the Archive drives work so well, but like I mentioned there are other reports of these models being slow.

 

Somehow i feel there has to some other reason. I started preclear as someone suggested in Seagate * TB thread and just wanted to check the speed. Currently it is 3% done but it is average speed is showing as 180MBPS.   If preclear can run at this speed then why not my standard writes from windows to Unraid over LAN CAT6 cable ? My file sizes are also not just 1 GB rather generally they are of size 2-3 GB in general. 

 

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7 hours ago, ManishGupta8 said:

 

Somehow i feel there has to some other reason. I started preclear as someone suggested in Seagate * TB thread and just wanted to check the speed. Currently it is 3% done but it is average speed is showing as 180MBPS.   If preclear can run at this speed then why not my standard writes from windows to Unraid over LAN CAT6 cable ? My file sizes are also not just 1 GB rather generally they are of size 2-3 GB in general. 

 

Precelar only writes zeros, and that can be handled different by the firmware, i.e., not hit the SMR wall, you should just test with the other disks, it would confirm if the issues are the disks nor not.

 

5 hours ago, trurl said:

Preclear will always be faster than writes to the parity array because parity has to update also. Please read this post to get a better understanding of the way the 2 modes for parity updates works:

Currently the OP is using a single data disk plus parity, so Unraid works as raid1, no parity speed penalty.

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6 hours ago, johnnie.black said:

Precelar only writes zeros, and that can be handled different by the firmware, i.e., not hit the SMR wall, you should just test with the other disks, it would confirm if the issues are the disks nor not.

 

Currently the OP is using a single data disk plus parity, so Unraid works as raid1, no parity speed penalty.

So Are we concluding that its definitely Hard Disk fault ??

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22 hours ago, johnnie.black said:

No, we are waiting for you to test with different disks, like you said.

Interesting...I Started Preclear on both 8 TB Disks that i got from Costco at same time...Currently both are running (in N54L with 8 GB RAM) but i can see huge difference  in speed. Preclear is not yet completed but see the current status....

 

 

 

 

Disk1_Speed.JPG

Disk2_Speed.JPG

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On 12/14/2018 at 8:39 AM, johnnie.black said:

No, we are waiting for you to test with different disks, like you said.

Hi Johnie and Turyl,

 

As you suggested I have done some test and I was wondering if you can share your inputs on same. Below is a brief summary of what i have done so far.

 

  1. Purchased two 8 TB Seagate Hard Drives from Costco At Same time.
  2. Both are connected to Proliant N54L with 8 GB RAM exactly in same way via SATA Connector (both connected to Motherboard via same SAS connector)
  3. There are no other Hard Disks connected to Proliant machine as of now except these 2. 
  4. Unraid ver 6.6.6 was installed alongwith Community applications and PreClear Disk (from gfjardim's plugin Repository)
  5. I started preclear on both hard disk almost at same instant.
  6. Disk 1 Took in total  under 47 hrs to finish preclear. Out of these 47 Hrs it took rought 15 hrs for Step 2 i.e. "Zeroing the Disk" at average speed of 144MB/sec. Screenshot attached below.
  7. Disk 2 has already taken 66+ hrs and still preclear is not finished. Out of 66+ hrs it has consumed 51 hrs in Step 2 and still only 58% completed. Step 2 is running at average speed of 25MB/sec.Screenshot attached below.

 

I am feeling as if I have just got one of the bad hard disk (Disk 2) which is causing this issue but other hard disk (Disk 1 ) is correct.

 

Can you guys please share your views on same ?

 

 

 

Disk1_Speed.JPG

Disk2_Speed.JPG

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2 minutes ago, johnnie.black said:

Preclear has been known to show wrong stats and/or clear disks at different speeds when clearing multiple disks, though the results appear to confirm your issue nothing like replacing the slower disk and test to confirm.

Thanks. So are you suggesting to cancel currently running preclear and do the same again but this time only on the disk which is running slow as per preclear ?

 

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On 12/15/2018 at 7:40 AM, ManishGupta8 said:

Interesting...I Started Preclear on both 8 TB Disks that i got from Costco at same time...Currently both are running (in N54L with 8 GB RAM) but i can see huge difference  in speed. Preclear is not yet completed but see the current status....

 

 

 

 

Disk1_Speed.JPG

Disk2_Speed.JPG

 

Hi Johnie and Turyl,

 

Here are the Stats when i ran preclear on new 8 TB Disk. Still Slow as compare to 1 st preclear result but much better than previous 8 TB Hard Disk.

 

 

Should I run preclear again on both Disk 1 and Disk 3 together again 2nd time ?

 

 

Disk3_PreClear.JPG

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19 minutes ago, johnnie.black said:

64MB/s average is still rather slow, but you can try using that disk in the array together with the previous fastest one, if writes speeds are now around 60MB/s instead of 25MB/s you know the disks are the problem.

So far i have done preclear only 2 times on Parity and 1 time on Data Disk (Disk 3). Before I add them to array do you suggest to do preclear again 22-3 times ?

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