AS-5110: Limited RAID 6 volume size or drive count?

[joelang1699]

Only capable of 24TB? A 10 bay NAS using 6TB drives in RIAD 6 is well above that figure not to mention its not a problem in competitors products!

Thats a bit of an issue for me as the whole point is I need as many bays as possible using 6TB drives. Redundancy isnt a big issue for me as I have the main NAS in RAID 6, a backup NAS of the same capacity in RAID 6 and hopefully the 5110 will serve as another off site backup.

[orion]

Only capable of 24TB? A 10 bay NAS using 6TB drives in RIAD 6 is well above that figure not to mention its not a problem in competitors products!

Thats a bit of an issue for me as the whole point is I need as many bays as possible using 6TB drives. Redundancy isnt a big issue for me as I have the main NAS in RAID 6, a backup NAS of the same capacity in RAID 6 and hopefully the 5110 will serve as another off site backup.

AS-5 can actually support file system up to 1EB. The maximum file size is 16TB. That's 64-bit ext4 file system. Ok, as far as I know, AS-2 and AS-3 should have file system up to 16TB only (according to information from asustor support). Asustor configures these two series as 32-bit option on ext4 file system parameters. I don't know the reason (maybe, performance is a factor).

[Kapitein Haak]

I don't know the reason (maybe, performance is a factor).

My AS304 is equipped with a 32-bit processor (CE5335) which most likely is the limitation for 16TB volumes (both the AS2 and AS3 series have a 32 bit CPU)

[orion]

My AS304 is equipped with a 32-bit processor (CE5335) which most likely is the limitation for 16TB volumes (both the AS2 and AS3 series have a 32 bit CPU)

Yes, AS-304T is equipped with a 32-bit CPU. But I wonder if 32-bit CPU can deal with 64-bit extend structure on ext4 (actually 48-bit block address). I believe 32-bit CPU should be capable for it, but certain performance penalties. However I'm not sure if linux ext4 kernel code can deal with it.

[Kapitein Haak]

Hello Orion,

I wasn't sure of the kernel code too (and was still hoping to go over the 16TB as disks are getting very large today). But I found http://forum.synology.com/enu/viewtopic.php?f=7&t=96310 where someone actually emptied his Synology to test this.

The next challenge is mounting the newly created filesystem, and it is here that we run into the real problem:

DiskStation> mount -t ext4 /dev/md2 dummy
mount: mounting /dev/md2 on dummy failed: File too large
DiskStation> dmesg | tail -1
[ 959.280251] EXT4-fs (md2): filesystem too large to mount safely on this system

As it turns out, this message is generated by the Linux kernel. It flat-out refuses to mount the newly minted filesystem.

On StackOverflow I found this remark:

http://serverfault.com/questions/462029 ... 8tb-raid-6

which says: 32 bit kernels are limited to 16 TiB because the page cache entry index is only 32 bits.

This appears to be on a DS415, which is close to our AS-304T. So, not a definitive NO to larger then 16TB volumes, but changes are very slim they will be supported.

[orion]

Hello Kapitein Haak,
Thanks for the precise information. It turns out that linux 32-bit kernel code does not support 64-bit cache addressing. I think there are no reasons that linux kernel group will support the changes (64-bit CPU are cheaper and cheaper). So 32-bit linux (on my AS-304T ) does not support file system larger than 16TB.

[jchny]

Mike, Elrique, Joe, and anyone else who helped...

Just wanted to post a follow up message. I bought the AS-5110 from ExcaliburPC, along with eight 3TB drives, back in April. I received it, set it up, then shipped it to the film lab (Bollinger & Rutter in PA) who loaded it up with the first 4 or 5 TB of files and then brought it back to me. The box and drives survived the UPS shipping (very well packed) and are performing flawlessly.

I'm very happy with it. I took the good advice received on this forum and set up two drives as a RAID 1 LUN and six drives as a RAID 6 LUN. That gives me plenty of space for my transferred old home movies (from 16mm and Super 8) in a very fat scanning format, with over 1GB per minute of film.

No complaints. Thanks to the forum members who gave good advice to this RAID newbie...