Earlier quoted context omitted.
You're right about their cross-rack RAID-like stack, but didn't Backblaze switch to ext4 in the meantime?
possibly... cant see anything about it on storage pod 6 [1] but i do remember mentioning a file system, i just though it was XFS... [1]: https://www.backblaze.com/blog/open-source-data-storage-serv...
https://www.backblaze.com/pod.html says ext4.
https://www.backblaze.com/blog/vault-cloud-storage-architect...
Each of the drives in a Vault has a standard Linux file system,
ext4, on it. This is where the shards are stored. There are
fancier file systems out there, but we don’t need them for
Vaults. All that is needed is a way to write files to disk, and
read them back. Ext4 is good at handling power failure on a
single drive cleanly, without losing any files. It’s also good at
storing lots of files on a single drive, and providing efficient
access to them.
Diagnose and repair file system problems with JFS and ext4 and debug
other system problems
We upgraded the Linux 64-bit OS from Debian 4 to Debian 5, but we
no longer use JFS as the file system. We selected JFS years ago
for its ability to accommodate large volumes and low CPU usage,
and it worked well. However, ext4 has since matured in both
reliability and performance, and we realized that with a little
additional effort we could get all the benefits and live within
the unfortunate 16 terabyte volume limitation of ext4. One of the
required changes to work around ext4’s constraints was to add
LVM (Logical Volume Manager) above the RAID 6 but below the file
system. In our particular application (which features more writes
than reads), ext4’s performance was a clear winner over ext3,
JFS, and XFS.