On 05/04/2021 18:46, David T-G wrote:
Wol & Roger, et al --
...and then antlists said...
%
% On 05/04/2021 12:30, Roger Heflin wrote:
% >> diskfarm:~ # grep /mnt/ssd /etc/fstab
% >> LABEL=diskfarm-ssd /mnt/ssd xfs defaults 0 0
% >>
% >>will work for my bitmap files target, since all I see is that it must be
% >>an ext2 or ext3 (not ext4? old news?) device.
%
% Bear in mind you're better off using a journal (and bitmaps and
% journals are incompatible).
A journal of the filesystem (XFS or ReiserFS) on the RAID5 device? Or a journal
of the actual md?
Journal of the md. I'm thinking raid journal, which fixes the raid-5
write hole (I don't understand it, but if a system crashes in the middle
of a raid-5 write it can apparently mess things up something horrid).
diskfarm:~ # df -kh /mnt/4Traid5md/ /mnt/750Graid5md/
Filesystem Size Used Avail Use% Mounted on
/dev/md0p1 11T 11T 309G 98% /mnt/4Traid5md
/dev/md127p1 1.4T 1.4T 14G 100% /mnt/750Graid5md
diskfarm:~ # mount | grep /dev/md
/dev/md0p1 on /mnt/4Traid5md type xfs (rw,relatime,attr2,inode64,logbufs=8,logbsize=32k,sunit=1024,swidth=2048,noquota)
/dev/md127p1 on /mnt/750Graid5md type reiserfs (rw,relatime)
%
...
% >I am about to do some array reworks to go from all 3tb disks to start
% >using some 6tb disks. If the file was pre-allocated I would not
...
% >
% Umm... don't use all the space on your 6TB disks. I'm planning to
% build my arrays on dm-integrity, which will make raid 5 a bit more
% trustworthy.
[snip]
Oooh, something else to learn :-) I hope to go from 4 drives to 6 when I
do, and I'll be buying the best GB/$ at the time, but it will also be a
grow-over-time thing.
dm-integrity is nothing to do with raid per-se, but it does a checksum
of the data on disk. If your data is corrupted (rather than lost)
there's no way you can get it back with raid-5. dm-integrity turns
corruption into data loss allowing raid-5 to recover.
Read my journey building my new system ... :-)
https://raid.wiki.kernel.org/index.php/System2020
I've got a little more to add, but it's stalled for the perennial
problem of finding time to do and concentrate.
Cheers,
Wol
