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preclear/setup questions


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Hi, My name is Mark is this is my first (actually my second) post. I've been lurking here for the last two months while I evaluated my media server options. My quest started by looking for a backup solution to my family photos, home videos, and music. It started by looking at an attached external drive; then a NAS; then I found reference to unRaid on AVS. What started as a backup solution quickly evolved into wanting a media server and a whole house wired network.  ;D

 

I finally got enough pieces together to try out the free version of unRaid. I fully plan to buy the pro license once I feel comfortable with setting up unRaid. Here is what I have put together:

Antec Sonata II case (what I had on hand, should support 9 drives).

Corsair CX430 PS

Biostar TA890GXB-HD (6 onboard SATA III, GigE)

Sempron 140

2GB DDR3 stick value ram

2TB Hitachi 7200 Deskstar (parity)

2TB Seagate 5900 LP x2 (data)

 

I have unRaid running (only have the parity assigned and unMenu installed).

 

Finally to my question:

I ran preclear on my first Seagate (results below). I originally assumed that I only needed to run this once, but have since seen reference to people running preclear multiple times (4+). How many times should I run this? Please take a look at my results and let me know what they mean.

 

Thanks for your time and help,

Mark

 

Preclear 1:
===========================================================================
=                unRAID server Pre-Clear disk /dev/sdb
=                       cycle 1 of 1
= Disk Pre-Clear-Read completed                                 DONE
= Step 1 of 10 - Copying zeros to first 2048k bytes             DONE
= Step 2 of 10 - Copying zeros to remainder of disk to clear it DONE
= Step 3 of 10 - Disk is now cleared from MBR onward.           DONE
= Step 4 of 10 - Clearing MBR bytes for partition 2,3 & 4       DONE
= Step 5 of 10 - Clearing MBR code area                         DONE
= Step 6 of 10 - Setting MBR signature bytes                    DONE
= Step 7 of 10 - Setting partition 1 to precleared state        DONE
= Step 8 of 10 - Notifying kernel we changed the partitioning   DONE
= Step 9 of 10 - Creating the /dev/disk/by* entries             DONE
= Step 10 of 10 - Testing if the clear has been successful.     DONE
= Disk Post-Clear-Read completed                                DONE
Disk Temperature: 41C, Elapsed Time:  29:05:36
============================================================================
==
== Disk /dev/sdb has been successfully precleared
==
============================================================================
S.M.A.R.T. error count differences detected after pre-clear
note, some 'raw' values may change, but not be an indication of a problem
54c54
<   1 Raw_Read_Error_Rate     0x000f   100   100   006    Pre-fail  Always                                                                                                 -       9855
---
>   1 Raw_Read_Error_Rate     0x000f   119   099   006    Pre-fail  Always                                                                                                 -       209554138
58c58
<   7 Seek_Error_Rate         0x000f   100   253   030    Pre-fail  Always                                                                                                 -       39
---
>   7 Seek_Error_Rate         0x000f   100   253   030    Pre-fail  Always                                                                                                 -       518382
64c64
< 188 Command_Timeout         0x0032   100   253   000    Old_age   Always                                                                                                 -       0
---
> 188 Command_Timeout         0x0032   100   100   000    Old_age   Always                                                                                                 -       0
66,67c66,67
< 190 Airflow_Temperature_Cel 0x0022   068   065   045    Old_age   Always                                                                                                 -       32 (Lifetime Min/Max 28/32)
< 195 Hardware_ECC_Recovered  0x001a   100   100   000    Old_age   Always                                                                                                
---
> 190 Airflow_Temperature_Cel 0x0022   059   057   045    Old_age   Always                                                                                                 -       41 (Lifetime Min/Max 28/43)
> 195 Hardware_ECC_Recovered  0x001a   053   047   000    Old_age   Always                                                                                                
70,73c70,73
< 199 UDMA_CRC_Error_Count    0x003e   200   253   000    Old_age   Always                                                                                                 -       0
< 240 Head_Flying_Hours       0x0000   100   253   000    Old_age   Offline                                                                                                -       163612484173844
< 241 Total_LBAs_Written      0x0000   100   253   000    Old_age   Offline                                                                                                -       0
< 242 Total_LBAs_Read         0x0000   100   253   000    Old_age   Offline                                                                                                -       1090
---
> 199 UDMA_CRC_Error_Count    0x003e   200   200   000    Old_age   Always                                                                                                 -       0
> 240 Head_Flying_Hours       0x0000   100   253   000    Old_age   Offline                                                                                                -       237533166305329
> 241 Total_LBAs_Written      0x0000   100   253   000    Old_age   Offline                                                                                                -       560459184
> 242 Total_LBAs_Read         0x0000   100   253   000    Old_age   Offline                                                                                                -       3055716227
============================================================================

 

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If you've not seen any sectors marked for re-allocation, or re-allocated, 1 pre-clear cycle is probably enough... 

 

The initial failures of hard-disks falls into a "bathtub curve"  You'll see most hardware failures in its first hours of operation with diminishing failures after that until many years later as mechanical wear takes its toll.

 

If you have the time, 3 or 4 cycles is not bad, but certainly, not necessary.  Your initial pre-clear cycle looks perfectly normal.

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If I'm reading the wiki correctly, then I do need to run the format option before using the new drive. Why is that necessary if I ran the pre-clear script first? Did I miss something?

 

Wiki excerpt:

Go back to the main unRaid management page, if the drives are new, or if they have any other file-system other than reiserfs, they will appear as "unformatted" You will need to check the checkbox to format them. this will erase any data that was previously on them by first clearing them and then partitioning and formatting them with a reiserfs file-system.

When this operation finishes, all the data disks, including the new one(s), will be exported (shared) on the lan and be available for use.

The format operation consists of two phases. First, the the entire contents of the new disk(s) is cleared (written with zeros), and then it’s marked active in the array. Next, a file system is created. unRAID Server uses the ReiserFS journalled file system.

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If I'm reading the wiki correctly, then I do need to run the format option before using the new drive. Why is that necessary if I ran the pre-clear script first? Did I miss something?

Clearing a drive writes zeros to it, and sets up the initial partition, but does NOT format it.  You must perform that step after you add the drive to the array so when you do format it the formatting is reflected in the parity calculations. 

 

If the formatting were to occur before you added the drive to the array it would no longer be only zeros, and it would mess up the existing parity calculations.  Formatting it after assigning it to the array allows the parity calcs to correctly reflect the data (and formatting) on the drive.

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Good God, I hope this is not typical write performance. This is from my laptop via wireless (g). I'm also downloading from the net at 1.15 MB/s. Am I looking at an unRAID write limit or wireless limit? I'm digging up a network cable now to see if it improves hardwired.

 

writespeed1.jpg

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OK, hardwired I'm up to 11MB/s. Doing a search through the forums, it looks like I should expect around 30MB/s write speed. Correct? If so, what should I look at as the possible bottleneck?

Your laptop.  It probably only has a 100Mb/s LAN connection, and that will get at best between 10 and 12 MB/s.  You are right on target.
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OK, hardwired I'm up to 11MB/s. Doing a search through the forums, it looks like I should expect around 30MB/s write speed. Correct? If so, what should I look at as the possible bottleneck?

Are you running on a 100 Mbit network by any chance? 11MB/s is near it's upper limit.

 

 

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Are you running on a Gigabit 1000mbit network with CAT 5e or CAT6 cables and Gigabit 100mbit network cards on the server and clients? Odds are you're only running a a 100mbit network. The 100mbit network has a maximum theoretical speed is 12 mbit, so your 11mbit is very typical.

 

 

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