Raid 50 - Hot swap question

[grayles]

My 16 bay raid 50 NAS is running out of space.

Is it possible to hot swap one drive at a time with a larger HDD?

 

[RMerlin]

That depends on your NAS's software. Check with the manufacturer if they support online capacity upgrades. Some, like QNAP, do.

 

[thiggins]

Be aware that expansion is a tedious process. The array must completely rebuild after each disk swap and you don’t get the expansion until all drives in the array have been swapped.

 

[RMerlin]

Be aware that expansion is a tedious process. The array must completely rebuild after each disk swap and you don’t get the expansion until all drives in the array have been swapped.

And it can be quite intensive on the array. It's not uncommon for a disk to fail in the array during those rebuilds, which means you have to be extra sure to have a complete backup before attempting such a procedure, especially when using large disk capacities, which are more susceptible in encountering read errors.

 

[sfx2000]

My 16 bay raid 50 NAS is running out of space.

Is it possible to hot swap one drive at a time with a larger HDD?

As others mentioned - it is possible, but it's time consuming and not without some level of risk - so make sure you have it backed up somewhere in case something goes wrong...

Check with the NAS vendor for specific steps on the process..

 

[grayles]

Thanks everyone for the opinions and suggestions.

Is the easiest solution to backup everything on a a huge backup drive then do the HDD upgrade to the NAS?

What are the usual methods to upgrade hard-drives? Do i simply fit them in after backing up the data and it will work out of the box? Or is there things I must do within the NAS after replacing all hardrives

 

[RMerlin]

Is the easiest solution to backup everything on a a huge backup drive then do the HDD upgrade to the NAS?

Depends on your needs.

A concrete example: a few months ago, one of my customers (an architectural design company of 30 employees) needed to upgrade the disks on their three disks RAID5 QNAP NAS. They were however in a work rush period, and couldn't afford the performance impact of a RAID 5 rebuild during the day. So, we had to do the swaps during weekends. Each disk swap required 12-14 hours to resync the mirror, so we ended up spreading the migration over the course of two or three weekends.

The final step required the whole raid to be taken offline for a number of hours - that's the step where the RAID capacity is actually increased.

Again, this was the procedure for QNAP. You have to check the exact procedure for your specific NAS model first (assuming they do allow inline capacity upgrades).


If your RAID has 10+ disks, then consider the amount of time it will take you do do the disk replacements, one disk at a time, waiting for a full RAID rebuild between each disk swaps... And that final step where the whole RAID will be offline for a number of hours. Can you afford that downtime? Is the NAS content mission-critical (i.e. used by a business), or just your personal collection of videos/photos/music?

With such a large array, I'd recommend having a complete up-to-date backup, scrapping and recreating a new RAID out of the new disks, then restoring the backup to the new RAID. If anything goes wrong with the restoration, then your plan B will be putting back all your original disks in the NAS, and fixing your backup / recovering any missing files, etc... So in a way, this gives you an extra security net in case something goes wrong. With an online upgrade, you will be dependent on your backup, AND the existing disks not failing mid-upgrade.

 

[RMerlin]

Just to provide more background info, why RAID5 is no longer recommended with large disk capacities: in their specifications, each disks will be rated for an average unrecoverable error rate (this will tell you how many bits can be read on average before an unrecoverable error is encountered, leading to potential data loss). The thing is, while disk capacities have increased over the years, that error rate has not. So if you have a 10 disks RAID array and you are replacing each disks one at a time, you will be doing 10 FULL disk reads on all of your disks. Multiply the capacity of each disk by 10, then see how it compares to the average error rate specified for those disks. Chances are you have a fairly high chance of encountering a read error...

And you can add to that the increased stress of doing 10 full disk reads, which will lead to increased temperature during the procedure. Aging disks will have an increased chance of dying during that procedure.

 

[RMerlin]

What are the usual methods to upgrade hard-drives? Do i simply fit them in after backing up the data and it will work out of the box? Or is there things I must do within the NAS after replacing all hardrives

The exact procedure is NAS-specific. In QNAP's case, it was even firmware-version specific. Took me a while to find up-to-date instructions, as the most commonly referred article was specific to older firmware versions. It's not just a matter of swapping disks, there are operations that must be done through the NAS's management interface to launch the entire process.