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Re: A question about X-RAID

kamanwu
Aspirant

A question about X-RAID

I have a 4 disk NAS.

 

For now, I have two 3T disks. (raid 1).

I plan to buy two 8T disks....

 

Basing on my understanding.   I will get 2 groups

Group 1 is raid 5 which gives me 9T.

1, 3T

2, 3T

3, 3T of 8T

4, 3T of 8T

 

Group 2 is raid 1 which gives me 5T

1, 0

2, 0

3, 5T of 8T

5, 5T of 8T

 

------

BUT I do not want this setup. I want:

Group 1 is raid 1 which gives me 3T

1, 3T

2, 3T

3, 0

4, 0

 

Group 2 is raid 1 which gives me 8T

1, 0

2, 0

3, 8T

4, 8T

 

---

I know I will get 11T in totall (3T less, that's OK).

Is that doable?  or it's impossible. 

 

Thanks a lot.

Message 1 of 13

Accepted Solutions
StephenB
Guru

Re: A question about X-RAID


@kamanwu wrote:

I was heard raid 5 is outdated. The perfermance is NOT good (compare with raid 1).  Also, becase of the way it works, there is a high chance 2 disk have issue at the same time.  (Is that true?)

 


The RAID mode doesn't increase the chances of two disks having problems at the same time.  And either way, you can lose data if two disks fail.  Though with two RAID-1 groups, there is protection against some two disk failures (in your proposal, one 3 TB and one 8 TB drive could fail with no loss).

 

Read performance on large files should be the same with RAID-5.  Write performance can be a bit slower due to the need to update the parity blocks.  With small files, the limit is usually the iops - which is fundamental to all mechanical disks.  The best way to increase performance there is to use SSDs.

 

But with a home NAS, the performance is usually limited by the gigabit network speed - not by the disk or RAID speeds.  It's quite different with enterprise servers and data centers - which either have the storage in the server itself or are using much faster networks (up to 100 gb/s).

 

FWIW, three of own NAS use XRAID/RAID-5 - volume sizes range from 20 to 30 TB.

 


@kamanwu wrote:

Here is the post I read: https://community.spiceworks.com/topic/545782-raid-5-unsafe-where-is-the-proof 


FWIW, I agree with the "where is the proof" comments. I don't find arguments based on URE statistics convincing - they generally take the URE specs in the drive datasheets as reality (which in my experience they aren't - I've seen very few UREs).  The older articles suggest that I shouldn't be able to do a resync on arrays the size I am running now - but I haven't had them fail. I also run quarterly scrubs - which are also essentially resyncs - and I haven't had issues with them either. 

 

That said, disks (and devices) do fail - and sometimes it can take a while for bad sectors on a disk to be detected (since in most cases there is a lot of data that isn't accessed all that often).  So you do need to have a back up plan in place for your NAS, no matter what RAID mode you use.  I also recommend using the maintenance schedule (on the volume tab) to periodically test the disks.  Personally I run one of the maintenance functions every month (cycling through all four 3 times a year).

 


@kamanwu wrote:

 I prefer ONE volumn which is 11T.  


Which amounts to RAID-10.

 

I haven't tried converting RAID-1 to RAID-10 manually with FlexRAID, but I think you can create a RAID-1 group on the larger disks, and concatenate it to the existing volume. 

 

You could also switch to FlexRAID, uninstall your apps, delete the volume, and create a new RAID-10 volume.  You'd need to reconfigure the NAS, reinstall the apps, and restore the data from backup.

 

Personally I think the main attraction of two RAID-1 volumes is that RAID recovery (if you ever need it) is much easier.  

 

In practice, there isn't much difference between two volumes and one when you are accessing the NAS with SMB.  Either way, you just see the list of shares when you access the NAS over the network.  You do need to roughly balance the storage, so you keep adequate free space on both volumes.  That would need some occasional adjustments (moving some shares or folders around).

 

 

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Message 5 of 13

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StephenB
Guru

Re: A question about X-RAID


@kamanwu wrote:

 

Is that doable?  or it's impossible. 

 


XRAID won't do it, but you might be able to do it with FlexRAID.  Though I am thinking that two RAID-1 volumes might be a better approach (and certainly can be done with FlexRAID).

 

What model NAS do you have?

 

Any particular reason for wanting this configuration?

Message 2 of 13
kamanwu
Aspirant

Re: A question about X-RAID


@StephenB wrote:

@kamanwu wrote:

 

Is that doable?  or it's impossible. 

 


XRAID won't do it, but you might be able to do it with FlexRAID.  Though I am thinking that two RAID-1 volumes might be a better approach (and certainly can be done with FlexRAID).

 

What model NAS do you have?

 

Any particular reason for wanting this configuration?


Thanks for the reply.

 

I have an old NAS (Pro 4) which has been updated to OS6 (6.9.4).  Can I use FlexRAID?

 

I was heard raid 5 is outdated. The perfermance is NOT good (compare with raid 1).  Also, becase of the way it works, there is a high chance 2 disk have issue at the same time.  (Is that true?)

 

Here is the post I read: https://community.spiceworks.com/topic/545782-raid-5-unsafe-where-is-the-proof 

Message 3 of 13
kamanwu
Aspirant

Re: A question about X-RAID

I have read the docment.  I think I could switch from X-RAID to FlexRAID.

So I could have two RAID 1 volumn. (3T and 8 T).  This is different from what I want. I prefer ONE volumn which is 11T.  I will think about it. Thanks.

 

 

 

 


Message 4 of 13
StephenB
Guru

Re: A question about X-RAID


@kamanwu wrote:

I was heard raid 5 is outdated. The perfermance is NOT good (compare with raid 1).  Also, becase of the way it works, there is a high chance 2 disk have issue at the same time.  (Is that true?)

 


The RAID mode doesn't increase the chances of two disks having problems at the same time.  And either way, you can lose data if two disks fail.  Though with two RAID-1 groups, there is protection against some two disk failures (in your proposal, one 3 TB and one 8 TB drive could fail with no loss).

 

Read performance on large files should be the same with RAID-5.  Write performance can be a bit slower due to the need to update the parity blocks.  With small files, the limit is usually the iops - which is fundamental to all mechanical disks.  The best way to increase performance there is to use SSDs.

 

But with a home NAS, the performance is usually limited by the gigabit network speed - not by the disk or RAID speeds.  It's quite different with enterprise servers and data centers - which either have the storage in the server itself or are using much faster networks (up to 100 gb/s).

 

FWIW, three of own NAS use XRAID/RAID-5 - volume sizes range from 20 to 30 TB.

 


@kamanwu wrote:

Here is the post I read: https://community.spiceworks.com/topic/545782-raid-5-unsafe-where-is-the-proof 


FWIW, I agree with the "where is the proof" comments. I don't find arguments based on URE statistics convincing - they generally take the URE specs in the drive datasheets as reality (which in my experience they aren't - I've seen very few UREs).  The older articles suggest that I shouldn't be able to do a resync on arrays the size I am running now - but I haven't had them fail. I also run quarterly scrubs - which are also essentially resyncs - and I haven't had issues with them either. 

 

That said, disks (and devices) do fail - and sometimes it can take a while for bad sectors on a disk to be detected (since in most cases there is a lot of data that isn't accessed all that often).  So you do need to have a back up plan in place for your NAS, no matter what RAID mode you use.  I also recommend using the maintenance schedule (on the volume tab) to periodically test the disks.  Personally I run one of the maintenance functions every month (cycling through all four 3 times a year).

 


@kamanwu wrote:

 I prefer ONE volumn which is 11T.  


Which amounts to RAID-10.

 

I haven't tried converting RAID-1 to RAID-10 manually with FlexRAID, but I think you can create a RAID-1 group on the larger disks, and concatenate it to the existing volume. 

 

You could also switch to FlexRAID, uninstall your apps, delete the volume, and create a new RAID-10 volume.  You'd need to reconfigure the NAS, reinstall the apps, and restore the data from backup.

 

Personally I think the main attraction of two RAID-1 volumes is that RAID recovery (if you ever need it) is much easier.  

 

In practice, there isn't much difference between two volumes and one when you are accessing the NAS with SMB.  Either way, you just see the list of shares when you access the NAS over the network.  You do need to roughly balance the storage, so you keep adequate free space on both volumes.  That would need some occasional adjustments (moving some shares or folders around).

 

 

Message 5 of 13
kamanwu
Aspirant

Re: A question about X-RAID


@StephenB wrote:


That said, disks (and devices) do fail - and sometimes it can take a while for bad sectors on a disk to be detected (since in most cases there is a lot of data that isn't accessed all that often).  So you do need to have a back up plan in place for your NAS, no matter what RAID mode you use.  I also recommend using the maintenance schedule (on the volume tab) to periodically test the disks.  Personally I run one of the maintenance functions every month (cycling through all four 3 times a year).

That's a good suggestion.  I will do it.

Just want to comfirm that the "test disk" task is scheduled on a volumn.  So if you let it do monthly it will test all 4 disks every month, right?

But you said: cycling through all four 3 times a year.  It means it will test only ONE disk every month? 

 

Thanks a lot.

Message 6 of 13
StephenB
Guru

Re: A question about X-RAID


@kamanwu wrote:

Just want to comfirm that the "test disk" task is scheduled on a volumn.  So if you let it do monthly it will test all 4 disks every month, right?

 


Correct.  It runs the extended smart test on each drive in the volume.

 


@kamanwu wrote:

But you said: cycling through all four 3 times a year.  It means it will test only ONE disk every month? 

 


The four volume maintenance functions are disk test, balance, scrub, and defrag.  So I run the disk test every 4 months.

 

Scrub also accesses every sector on all the disks, so I think it doubles as a disk test.  I space them out so that the disk test and the scrub are two months apart.

 

The defrag is the least useful (generally not needed with the NAS file system).  So you could potentially skip that one.

 

 

Message 7 of 13
Sandshark
Sensei

Re: A question about X-RAID

In a ReadyNAS with spinning drives, the difference in speed you will see with the change you want to make is very small and the impact on expantion capability is very large.  If you have true backup of your data, the (IMHO very over-stated) potential for failure shouldn't be a significant factor on a home NAS.

 

My backup NAS are 12-drive RAID5 and my primary has two 12-drive RAID6.  All the hardware is identical.  The read and write speeds are also pretty much identical (they vary form test to test, so it's hard to assess perfectly).

 

I believe the stuff you are reading is folks picking nits that have little consequence in the real world, and especially in the use of a typical NAS. 

Message 8 of 13
kamanwu
Aspirant

Re: A question about X-RAID

 

Lots of things learned today.

 

I read this about scrubbing: https://kb.netgear.com/26941/ReadyNAS-OS-6-An-overview-of-relevant-scheduled-maintenance-tasks-avail...

I read this about bit-rot: https://kb.netgear.com/26091/Bit-rot-Protection-and-Copy-on-Write-COW-in-depth

 

Just checked my shares, I did not turn on "bit rot protection (copy-on-write)".

I need read more to decide if I need turn it on.

 

Thanks for the reply.

Message 9 of 13
Sandshark
Sensei

Re: A question about X-RAID

A lot depends on your specific use case, so it's hard to make a blanket recommendation.  For most home users, I believe it's beneficial. It and scrubs are especially important if your NAS contains archival data -- stuff you don't access often but care about.  Note that, as noted in the KB, COW protection will not be applied to existing files when you turn it on.  You'd have to manually re-write the files after COW is enabled.

 

FYI, those have little to do with XRAID.  They are part of BTRFS, about which you can read up on in non-Netgear forums as well.

Message 10 of 13
StephenB
Guru

Re: A question about X-RAID


@Sandshark wrote:

 

FYI, those have little to do with XRAID.  They are part of BTRFS, about which you can read up on in non-Netgear forums as well.


Bit-rot protection is a proprietary Netgear feature - not just part of BTRFS. 

 

Normally RAID can only recover data if the missing (or incorrect) data blocks are known.  Bit-rot protection uses a combination of BTRFS checksums and RAID parity to attempt to figure out what data is incorrect, and then uses RAID parity to fix it.  It doesn't always succeed (I had one case where a file somehow did get corrupted, but the feature couldn't fix it).

 

Though not perfect, it is a nice feature.  

Message 11 of 13
kamanwu
Aspirant

Re: A question about X-RAID


@Sandshark wrote:

 Note that, as noted in the KB, COW protection will not be applied to existing files when you turn it on.  You'd have to manually re-write the files after COW is enabled.

 

 


What is "manually re-write"? 

Can I just "mv" all files out, and "mv" them back? 

Message 12 of 13
Sandshark
Sensei

Re: A question about X-RAID

Di you read that part of the KB?

 

"Manually re-write" means issue commands to re-write (copy).  mv doesn't re-write unless it's between shares.  cp does.

 

cp file1 file2

rm file1

mv file2 file1

 

Now you've re-written file1.

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