I am new of snapraid and I would like to better understand some topic before strarting using it?
I would like to ask you help.
I have an HP MicroServer Gen8 with 4 bays. There are 2 x 6TB disks and 2 x 4TB disks. Currently, I'm using 1 x 6TB and 1 x 4TB for data and rsync for backup using the other disks interchangeably. Since I'm interested in integrity/scrub control, I'm seriously considering using snapraid. However, there are some things I can't understand. I've tried asking and finding answers on the web, but with little success. I kindly ask for your support, if possible.
I have the following questions:
1) I could use 6TB + 4TB + 4TB for data and 6TB for parity. However, I don't understand how a 6TB disk can provide parity for 14TB. Does this mean that data is also saved on the data disks (and not just in the parity disk)? At this point, my question is, how much actual data space would I have available for data considering the scenario described above, 6TB + 4TB + 4TB for data and 6TB for parity?
2) I understood I can use snapraid at any time. However currently I am using a pair of disks synchronized with rsync (6TB -> 6TB and 4TB -> 4TB). How do I switch to snapraid? Do I need to format the backup diskes of 1x6TB and 1x4TB to use as parity? Infact, I would like to have a parity for the 6TB data disk and parity for the 4TB disk. Additionally, I plan to make an external backup with restic for the 6TB disk, which contains important data. The question is, should I format the backup diskes of 1x6TB and 1x4TB or I can just staring using snapraid as the data between data and backup diskes are matching (backup has the same files of data disk)?
Thanks you very much
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1 parity disc can protect any number of data disks, although as the number of discs grows you want more parity to protect against simultaneous disk failure. Number of parity disck = number of failed disks you can recover from. The FAQ has recommendations for the number of parity disks.
It works because all the data disks cooperate when parity is calculated and all will cooperate if you need recovery. Articles on raid and parity will have details and diagrams.
The parity disk(s) must as large or larger than your largest data disk. So you will start with 1 6TB as parity for your 6 and 4 TB data disks. You do not make parity on a 4TB disk in this case.
To begin you need an empty 6TB and designate it as the first parity drive. Add data disks as needed (up to 6TB size each) and more parity (6TB or larger) as your array grows.
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Please could you confirm if I undersdood well when you said "The parity disk(s) must as large or larger than your largest data disk. So you will start with 1 6TB as parity for your 6 and 4 TB data disks. You do not make parity on a 4TB disk in this case.". You meant to create disks data with 6+4+4tb and 6tb of parity?
Do you thing is stupid to do 6tb disk of data and 6tb of parity and and another disk of 4tb of data with 4 tb parity?
if I create a syatem with 6+4+4tb of data (14tb) and 6 tb of parity, how much space I will have for data, considering only 6tb of parity?
Thank you very much one more time for your help!!!
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You have 6TB of parity, not 6 + 4. The 6TB will protect any number of disks as long as they are 6TB and smaller. (Later you will add more parity disks for safety, as described in the FAQ).
With 1 parity disk you can recover from the loss of 1 disk, data or parity. If you lose 2 disks at once you are in trouble.
"if I create a system with 6+4+4tb of data (14tb) and 6 tb of parity, how much space I will have for data, considering only 6tb of parity?"
You will have 14TB of data space. The parity disk(s) should be used for nothing else, just parity.
If that seems impossible: to create a block of parity the "same" block is read from each data disk and used to calculate the parity content. That block from a data disk can be reconstructed by applying a formula from the parity block and the original blocks on the remaining data disks.
Imagine all the data disks being read in parallel and the blocks from each used to create a block of parity. All the disks cooperate in parity creation and data recovery.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Dear Comunity,
I am new of snapraid and I would like to better understand some topic before strarting using it?
I would like to ask you help.
I have an HP MicroServer Gen8 with 4 bays. There are 2 x 6TB disks and 2 x 4TB disks. Currently, I'm using 1 x 6TB and 1 x 4TB for data and rsync for backup using the other disks interchangeably. Since I'm interested in integrity/scrub control, I'm seriously considering using snapraid. However, there are some things I can't understand. I've tried asking and finding answers on the web, but with little success. I kindly ask for your support, if possible.
I have the following questions:
1) I could use 6TB + 4TB + 4TB for data and 6TB for parity. However, I don't understand how a 6TB disk can provide parity for 14TB. Does this mean that data is also saved on the data disks (and not just in the parity disk)? At this point, my question is, how much actual data space would I have available for data considering the scenario described above, 6TB + 4TB + 4TB for data and 6TB for parity?
2) I understood I can use snapraid at any time. However currently I am using a pair of disks synchronized with rsync (6TB -> 6TB and 4TB -> 4TB). How do I switch to snapraid? Do I need to format the backup diskes of 1x6TB and 1x4TB to use as parity? Infact, I would like to have a parity for the 6TB data disk and parity for the 4TB disk. Additionally, I plan to make an external backup with restic for the 6TB disk, which contains important data. The question is, should I format the backup diskes of 1x6TB and 1x4TB or I can just staring using snapraid as the data between data and backup diskes are matching (backup has the same files of data disk)?
Thanks you very much
1 parity disc can protect any number of data disks, although as the number of discs grows you want more parity to protect against simultaneous disk failure. Number of parity disck = number of failed disks you can recover from. The FAQ has recommendations for the number of parity disks.
It works because all the data disks cooperate when parity is calculated and all will cooperate if you need recovery. Articles on raid and parity will have details and diagrams.
The parity disk(s) must as large or larger than your largest data disk. So you will start with 1 6TB as parity for your 6 and 4 TB data disks. You do not make parity on a 4TB disk in this case.
To begin you need an empty 6TB and designate it as the first parity drive. Add data disks as needed (up to 6TB size each) and more parity (6TB or larger) as your array grows.
Hi Bill, thank you so much for your answer.
Please could you confirm if I undersdood well when you said "The parity disk(s) must as large or larger than your largest data disk. So you will start with 1 6TB as parity for your 6 and 4 TB data disks. You do not make parity on a 4TB disk in this case.". You meant to create disks data with 6+4+4tb and 6tb of parity?
Do you thing is stupid to do 6tb disk of data and 6tb of parity and and another disk of 4tb of data with 4 tb parity?
if I create a syatem with 6+4+4tb of data (14tb) and 6 tb of parity, how much space I will have for data, considering only 6tb of parity?
Thank you very much one more time for your help!!!
You have 6TB of parity, not 6 + 4. The 6TB will protect any number of disks as long as they are 6TB and smaller. (Later you will add more parity disks for safety, as described in the FAQ).
With 1 parity disk you can recover from the loss of 1 disk, data or parity. If you lose 2 disks at once you are in trouble.
"if I create a system with 6+4+4tb of data (14tb) and 6 tb of parity, how much space I will have for data, considering only 6tb of parity?"
You will have 14TB of data space. The parity disk(s) should be used for nothing else, just parity.
If that seems impossible: to create a block of parity the "same" block is read from each data disk and used to calculate the parity content. That block from a data disk can be reconstructed by applying a formula from the parity block and the original blocks on the remaining data disks.
Imagine all the data disks being read in parallel and the blocks from each used to create a block of parity. All the disks cooperate in parity creation and data recovery.