N7700: Question about HD stacking

[nas_user]

hi forum

i have 6x 1TB HDD's in my N7700. my plan was to wait until the 2TB HDD become cheaper and use the 7th slot to start migration to 2TB HDD's. the plan was to migrate the raid5 after the new 2TB HDD is build in and after that remove one of the 1TB HDD and replace it also with a 2TB HDD. this procedure would be repeatet until all 1 TB HDD's are replaced.

my question now is: are there any concerns about this idea? i use a Raid5 with ZFS.

i dont have a chance to backup all that data ;-)

[philhu]

Well, based upon this units track record, there is a GOOD CHANCE you will have a drive fail during the rebuild 6 times.

I tried to do that, and failed on he 4th disk

Remember, when you pull the drive to force the rebuild you IMMEDIATELY lose all redundancy during the rebuild, which on my system took 16 hours a DISK. That was very bad

FYI

Best to do is buy a second system, put the 2tb disks in it and copy your data over.

[remoh]

Well, based upon this units track record, there is a GOOD CHANCE you will have a drive fail during the rebuild 6 times.

I tried to do that, and failed on he 4th disk

Remember, when you pull the drive to force the rebuild you IMMEDIATELY lose all redundancy during the rebuild, which on my system took 16 hours a DISK. That was very bad

FYI

Best to do is buy a second system, put the 2tb disks in it and copy your data over.

I have a N8800, quite similar to N7700. I would NOT recommend using RAID5 at all. I use 2TB Disks. Rebuild time about 18 hrs. Not acceptable to a have the risk of loosing all that long. Remember that all other disks will be under heavy use while rebuilding ! I use RAID6 and can't see a big impact on performance.

[philhu]

Yes, RAID 6 is a good start.

If you look at the error rates on disks, and realized during a rebuild, that it read/writes THE ENTIRE surface of all disks, the chance of a failure on one of the 5 other disks, based upon HD failure rates, is 35% or something obscene like that

You then do that 6 times, and I can almost GUARANTEE you'll see a disk fail during the process.

[nas_user]

thanks for your input - is really helpfull. iam not sure what to do now. but this for sure: its not an option to buy another NAS.

i started with 3 disks and migrated every time i added a new HDD. the two times run without trouble ... and if i add the 7th HDD - even with a 1TB version - it has to run again.

iam clueless now :-/

[quagmire]

you have at most 6 TB of data. take 3 2TB drives and move your data to them. remove all drives from your Thecus and replace with empty 2TB drives. copy data to them. Then install the remaining ( now empty) drives and let the Thecus do it's thing. Only one rebuild required.

[philhu]

That would be my plan too.

Take 3 2tb drives, copy your data to them

Put the other 3 2tb drives in the raid, rebuild it, copy the data to them

Then add the 3 drives and let it migrate/build one time


MAKE IT A RAID 6!