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Adding Hard Drives to RAID array.

SysEngJF
Aspirant

Adding Hard Drives to RAID array.

I was looking this up in other areas within Netgear, but the best I got was general info, including the following, about what configuration X-RAID uses on installed drives:

 

1-2 HDD: RAID-1 (unprotected if drives < 2 )

3-6 HDD: RAID-5

7-8 HDD: RAID-6

 

I do know that the ReadyNAS automatically picks the corresponding array based on how many drives you start with. My questions are:

 

1) Does the device dynamically reconfigure the array once a drive is installed to meet the requirements of the next array level? (i.e. installing a third or seventh disk, thereby satisfying the requirements for a RAID-5 or RAID-6, respectively.)

2) If yes, does it reformat the array in the process, or is the data kept intact while X-RAID makes the changes?

 

I'm running ReadyNAS OS 6.10.4 Hotfix 1, thinking of adding drives 1 or 2 at a time over the next few weeks.

Model: RN628X|ReadyNAS 628X - Ultimate Performance Business Data Storage - 8-Bay
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StephenB
Guru

Re: Adding Hard Drives to RAID array.


@SysEngJF wrote:

 

As far as auto-add and hot insert, I had read about that... though the docs I read seem a bit dated (they make it sound like it keeps the existing array, and I'd very much like to get it to RAID-6 once I hit that seventh drive). To add to the previous point, if the RN628X keeps the array as RAID-5 after the 7th disk is inserted (while online), then that would be a concern I'd need to know beforehand.

The data remains intact throughout the process, including the conversion to RAID-6 when the 7th disk is inserted.

 


@SysEngJF wrote:

I heard of Red Plus, yet those seem rare compared to Red Pro.

Originally there was just Red and Red Pro.

 

But after the strong backlash when folks found out that WD had been rolling out SMR w/o telling folks, WD divided the Reds into a new Red Line (only SMR) and Red Plus (CMR).  At this point there are a lot of WD Red Plus models - I haven't looked into availability.  The current list is here: product-brief-western-digital-wd-red-plus-hdd.pdf 

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StephenB
Guru

Re: Adding Hard Drives to RAID array.

What drives are you considering? I recommend not using desktop drives (or shucked USB drives) - many are SMR.  Instead use NAS purposed or enterprise class. I recommend against the (rebranded) WD Reds, as they are SMR, and have caused problems in ReadyNAS systems.  Red Plus (and Seagate Ironwolf) are CMR.  

 

Also, it often is cheaper to go with fewer, but larger drives - and that leaves slots open for cost-effective expansion later.  XRAID can handle mixed sizes - the capacity rule for single redunduncy is "sum the drives and subtract the largest"; for dual redundancy you subtract the largest two.  Note you will waste space if the largest 2 disks (4 disks with dual redundancy) aren't the same size.

 

 

As an aside, it can be much faster to power down, insert all the drives, then do a factory default -  even though you need to reconfigure the NAS from scratch, and reload the data from backup.  The reason is that the NAS is only syncing the array once - but on-line expansion from 1 to 8 drives requires it to resync seven times. 

 

If you (for example) want 8x10 TB, then building the array via factory default requires at 80 TB of disk I/O to create the array plus whatever I/O is needed to load the data.  But if you expand from 1x10TB to 8x10TB sequentially, it requires 350 TB of disk I/O (20+30+40+50+60+70+80).

 

Of course if you do rebuild from scratch, the NAS will be offline for a while.

 


@SysEngJF wrote:

 

1) Does the device dynamically reconfigure the array once a drive is installed to meet the requirements of the next array level? (i.e. installing a third or seventh disk, thereby satisfying the requirements for a RAID-5 or RAID-6, respectively.)

 


Yes.  You hot-insert the drive, and if it is blank the system will automatically add it to the array.  

 

You can power down, insert the drive, and power up again too, but I recommend hot-insert instead.  The system has to figure out what changed if you cold-insert, but sees the insertion even when you hot-insert.

 

If the drive is not blank, then you will need to explicitly format it using the format control of the volume tab.  That is a data safety feature (many folks mistakenly thought they could just plug in their NTFS-formatted hard drives, and were shocked when their data was lost).

 

New drives need to be at least as large as the largest one already in the array (that's not quite correct, but following this rule will always work). 

 


@SysEngJF wrote:

 

2) If yes, does it reformat the array in the process, or is the data kept intact while X-RAID makes the changes?

 


Data is kept intact.  System performance (as you might expect) will be reduced during the resyncs.

 


@SysEngJF wrote:

 

I'm running ReadyNAS OS 6.10.4 Hotfix 1, thinking of adding drives 1 or 2 at a time over the next few weeks.


The system processes one at a time, and I recommend adding them that way when you are expanding the array.  Otherwise it can be tricky to tell what happened if expansion fails for some reason.

 

We do recommend having a backup before expanding, as sometimes things do go wrong.  The expansion process requires reading or writing every sector of the existing drives every time you add a disk.  Since the array is unprotected during expansion (with single redundancy), if a disk fails then the volume is completely lost.

Message 2 of 6
SysEngJF
Aspirant

Re: Adding Hard Drives to RAID array.

Thanks, @StephenB . I did some research and it comes down to either WD Red Pro or WD Gold, though I lean a little more towards Gold due to the good experiences I've had with them, plus I've heard Red Pro can be loud to the point of causing some level of concern. I heard of Red Plus, yet those seem rare compared to Red Pro.

 

I thought of the re-sync each time a drive is added, which is why I'm thinking of starting at 3-6 drives to start it off, then add #7 and #8 one at a time.

 

As far as auto-add and hot insert, I had read about that... though the docs I read seem a bit dated (they make it sound like it keeps the existing array, and I'd very much like to get it to RAID-6 once I hit that seventh drive). To add to the previous point, if the RN628X keeps the array as RAID-5 after the 7th disk is inserted (while online), then that would be a concern I'd need to know beforehand.

 

The only real-time experience I've had with XRAID is my previous RN214, in which I used 4x Seagate ES.4 drives, all same size, speed, and firmware. The ReadyNAS made a RAID-5 out of them (via X-RAID) and it worked like a charm.

 

Just to be on the same page, yes. I have made 2 backups of all the data I plan to transfer to the new RN628X box.

Message 3 of 6
StephenB
Guru

Re: Adding Hard Drives to RAID array.


@SysEngJF wrote:

 

As far as auto-add and hot insert, I had read about that... though the docs I read seem a bit dated (they make it sound like it keeps the existing array, and I'd very much like to get it to RAID-6 once I hit that seventh drive). To add to the previous point, if the RN628X keeps the array as RAID-5 after the 7th disk is inserted (while online), then that would be a concern I'd need to know beforehand.

The data remains intact throughout the process, including the conversion to RAID-6 when the 7th disk is inserted.

 


@SysEngJF wrote:

I heard of Red Plus, yet those seem rare compared to Red Pro.

Originally there was just Red and Red Pro.

 

But after the strong backlash when folks found out that WD had been rolling out SMR w/o telling folks, WD divided the Reds into a new Red Line (only SMR) and Red Plus (CMR).  At this point there are a lot of WD Red Plus models - I haven't looked into availability.  The current list is here: product-brief-western-digital-wd-red-plus-hdd.pdf 

Message 4 of 6
Sandshark
Sensei

Re: Adding Hard Drives to RAID array.

The OS actually converts the RAID type before it does the sync, as that's how MDADM works when changing the RAID type.  It's all automatic and you have to turn XRAID off if you don't want that  It converts a 2-drive RAID1 to a 3-drive RAID5 that is missing a drive (and thus has no redundancy), then it syncs the new drive to fill the gap.  Likewise, it converts a 6-drive RAID5 to RAID6, then does the sync of the 7th.  Though the interrim 6-drive RAID6 would seem like it should still have single redundancy, I'm not sure it does since the parity format is different for RAID6.

 

I found this from the developer of MDADM:

 

It is a very similar process that can now be used to convert a RAID5 to a RAID6. We first change the RAID5 to RAID6 with a non-standard layout that has the parity blocks distributed as normal, but the Q blocks all on the last device (a new device). So this is RAID6 using the RAID6 driver, but with a non-RAID6 layout. So we "simply" change the layout and the job is done

 

But he doesn't say if the "simple" process of changing the layout retains any redundancy as it does so.

 

You are actually best off starting with what space you think you will need for the immediate future (maybe a year), and adding drives as you need them.  That allows you to space them out over more time, which can help in preventing nearly simultaneous drive failures due to equal age of the drives, will probably reduce your cost as drives get cheaper over time, and allows you to switch to a larger drive size for the added ones if you find your space requirements are growing faster than you originally thought.

Message 5 of 6
StephenB
Guru

Re: Adding Hard Drives to RAID array.


@Sandshark wrote:

 

The OS actually converts the RAID type before it does the sync

 


Yes, but I don't think it is computing the Q blocks then (or the P blocks when it switches from RAID-1 to RAID-5).  I think that is done with the actual layout is changed (which is the resilvering step).

 

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