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--- hw:qnap [2017-06-28 22:15] – root
+++ hw:qnap [2021-11-29 00:16] (current) – limit info Manuel Frei
@@ Line 30: / Line 30: @@
 grep "^AllowTcpForwarding" /etc/config/ssh/sshd_config
 </code>
+===== Resize over 16TB =====
+I once ran into the problem, that I couldn't extend my volume over 16TB. I didn't know why, but I had to recreate it with a bigger size and it worked.
+The problem is shallowly described here: [[https://www.qnap.com/en/how-to/knowledge-base/article/16tb-storage-limitation|QNAP KB: 16TB Storage Limitation]]
+They say, you can extend the volume over 16TB if you created the volume with firmware 4.4.3 or later but they don't say, how to figure that out.
+So, what's the reason for this limit? It's the file system. The maximum number of blocks on ext4 was 2^32 (4294967296). Let's figure out, in what size this results.
+Check the block size.
+<code>
+[~] # tune2fs -l /dev/mapper/cachedev1 | grep "^Block size:"
+Block size:               4096
+</code>
+means 4096 bytes.
+Let's multiply this with the maximum number of blocks (2^32) and get the size in tera bytes.
+<code>
+>>> (2**32)*4096/1024**4
+.0
+</code>
+TB is the maximum size of an ext4 file system with a block size of 4KB. But why can you delete the volume and create it with a bigger size than 16TB?
+Let's check the filesystem features of the newly created volume.
+<code>
+[~] # tune2fs -l /dev/mapper/cachedev1 | grep "^Filesystem features:"
+Filesystem features:      has_journal ext_attr filetype needs_recovery extent 64bit flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize
+</code>
+The relevant feature is "64bit".
+https://man7.org/linux/man-pages/man5/ext4.5.html
+>64bit: Enables the file system to be larger than 2^32 blocks.
+This file system feature wasn't available in the kernel versions before firmware versions before 4.4.3.