How long does it take to add a parity disk to the array

[super电动王]

i have three harddrive in array,WD HC530 14t,WD HC550 16t＊2.If i add a parity disk，how long will it take?

What determines the parity time?Is the capacity and number of parity disks? Or the capacity and number of array disks？

 

if i have 28 array disks and two parity disks,An array disk is damaged.How long will it take to rebuild the array？

[itimpi]

The time is determined by the size of the largest parity drive.    Typically around 2-3 hours per TB as long as your disk controllers are not throughput limited.

 

With modern large drives you are likely to find the Parity Check Tuning plugin will help with minimising the impact on daily use of very long parity checks.

 

[super电动王]

2 hours ago, itimpi said:

The time is determined by the size of the largest parity drive.    Typically around 2-3 hours per TB as long as your disk controllers are not throughput limited.

 

With modern large drives you are likely to find the Parity Check Tuning plugin will help with minimising the impact on daily use of very long parity checks.

 

That is to say, as long as the size of parity disk is certain, no matter how many disks with array, the time required is the same？

[itimpi]

1 hour ago, super电动王 said:

That is to say, as long as the size of parity disk is certain, no matter how many disks with array, the time required is the same？

Yes in principle the number of data drives is not normally a major factor.

 

However, If the extra drives on a disk controller mean its throughput capability is exceeded it slows the process down thus extending the time.   In addition,  very slow processors the overhead of calculating parity2 (which is a much more complex calculation than used for parity1 can also mean that the CPU becomes a limiting factor.  I

 

It is also worth noting that the process slows down as the inner tracks on drives are reached as their throughput is then lower (less sectors per track that can be read in a single disk rotation).

[itimpi]

4 hours ago, super电动王 said:

if i have 28 array disks and two parity disks,An array disk is damaged.How long will it take to rebuild the array？

Just realised that I did not answer this bit.  In this case the time to rebuild a drive is determined by the size of the drive being rebuilt (at the same 2-3TB per hour estimate as used for the parity build) so if the disks are smaller than the parity drives it does not take as long.

 

Another way to look at it is that both processes involve writing to every sector on a drive so how quickly that can be done is the determining factor.

 

[super电动王]

1 hour ago, itimpi said:

Just realised that I did not answer this bit.  In this case the time to rebuild a drive is determined by the size of the drive being rebuilt (at the same 2-3TB per hour estimate as used for the parity build) so if the disks are smaller than the parity drives it does not take as long.

 

Another way to look at it is that both processes involve writing to every sector on a drive so how quickly that can be done is the determining factor.

 

You have been very helpful. Thank you very much. The explanation is very clear. It is very suitable for beginners to understand.

Do you think I need to copy the data in these three hard disks and save it in other hard disks before setting parity disks for these three hard disks?After all, these hard disks need dozens of hours of continuous reading and writing.

Is it risky to perform parity check without backup？

[itimpi]

24 minutes ago, super电动王 said:

You have been very helpful. Thank you very much. The explanation is very clear. It is very suitable for beginners to understand.

Do you think I need to copy the data in these three hard disks and save it in other hard disks before setting parity disks for these three hard disks?After all, these hard disks need dozens of hours of continuous reading and writing.

Is it risky to perform parity check without backup？

I would not bother as drives in good health should be able to take the load.   There is also the fact that copying the data elsewhere would put just as much (if not more) load on the drives.

 

Having said that, remember the parity is no substitute for backups - it is only about protecting you from disk failures (i.e. giving high availability).   There are lots of other ways to lose data that parity will not protect you from.    You should therefore always have backups of anything you cannot afford to lose. 

 

Many people do not bother to make backups of media files on the basis that even if the worse happens they could recover them even though it could be time consuming.  It is up to each user to decide what trade-offs they are prepared to make for convenience v safety.

 

[super电动王]

On 5/20/2022 at 6:40 PM, itimpi said:

I would not bother as drives in good health should be able to take the load.   There is also the fact that copying the data elsewhere would put just as much (if not more) load on the drives.

 

Having said that, remember the parity is no substitute for backups - it is only about protecting you from disk failures (i.e. giving high availability).   There are lots of other ways to lose data that parity will not protect you from.    You should therefore always have backups of anything you cannot afford to lose. 

 

Many people do not bother to make backups of media files on the basis that even if the worse happens they could recover them even though it could be time consuming.  It is up to each user to decide what trade-offs they are prepared to make for convenience v safety.

 

oh dude,finally,i built parity disk with 23hours.more quicker than we thought.maybe Enterprise hard disk play a key role.After all, its speed is much faster than those ordinary 5400 RPM hard drives.

at first,read and write speed up to 250mb/s.when built finished,the number is 130mb/s.average speed is 195mb/s.

 

i read your post about parity check tuning plugin,It is a perfect solution to the problem that the parity time is too long.and now,i become your bigfans.

i also noticed three options in setting//schedule.They are cumulative parity check,accumulation frequency and accumulation duration.It looks like a simplified version of your project.does this conflict with the plugin?

By the way, can you send me the download address of the plugin，for some reason,i can't open the CA.

[itimpi]

20 minutes ago, super电动王 said:

i read your post about parity check tuning plugin,It is a perfect solution to the problem that the parity time is too long.and now,i become your bigfans.

Great

21 minutes ago, super电动王 said:

i also noticed three options in setting//schedule.They are cumulative parity check,accumulation frequency and accumulation duration.It looks like a simplified version of your project.does this conflict with the plugin?

You can ignore those settings if the plugin is installed (I.e. setting them is irrelevant).   The plugin pre-dates those being available and it already makes sure that correct values are stored in the parity check history. 

 

23 minutes ago, super电动王 said:

By the way, can you send me the download address of the plugin，for some reason,i can't open the CA.

I have only been making it available via CA.   It is actually hosted on github and getting the .plg file from there and installing it via the Plugins tab will probably work.