On Tue, 2009-10-20 at 10:15 -0600, Andreas Dilger wrote: > > It is true that the MDT device can become full at some point, but this > happens fairly rarely given that most Lustre HPC users have very large > files, and the size of the MDT is MUCH smaller than the space needed for > the file data.
Indeed. For some (very) anecdotal experience, witness my own very small Lustre filesystem usage: $ lfs df UUID 1K-blocks Used Available Use% Mounted on mds1_UUID 18348668 1327240 15972852 7% /mnt/lustre[MDT:0] client-OST0000_UUID 20642428 14883944 4709844 72% /mnt/lustre[OST:0] client-OST0001_UUID 20642428 14908260 4685528 72% /mnt/lustre[OST:1] client-OST0002_UUID 20642428 15055492 4538296 72% /mnt/lustre[OST:2] client-OST0003_UUID 20642428 14905716 4688072 72% /mnt/lustre[OST:3] client-OST0004_UUID 20642428 14871520 4722268 72% /mnt/lustre[OST:4] filesystem summary: 103212140 74624932 23344008 72% /mnt/lustre $ lfs df -i UUID Inodes IUsed IFree IUse% Mounted on mds1_UUID 5242880 2109580 3133300 40% /mnt/lustre[MDT:0] client-OST0000_UUID 1310720 208666 1102054 15% /mnt/lustre[OST:0] client-OST0001_UUID 1310720 538201 772519 41% /mnt/lustre[OST:1] client-OST0002_UUID 1310720 388754 921966 29% /mnt/lustre[OST:2] client-OST0003_UUID 1310720 292766 1017954 22% /mnt/lustre[OST:3] client-OST0004_UUID 1310720 469037 841683 35% /mnt/lustre[OST:4] filesystem summary: 5242880 2109580 3133300 40% /mnt/lustre As you can see, my MDT, at just less than 20% of the size of my total OST storage is quite oversized (by 10x perhaps?) for the data I am storing, and I store lots of small files -- Lustre, kernel and other misc source trees. I don't do any striping however, which helps keep MDT usage lower. > If you are using LVM you can increase the size of the MDT device and > resize the filesystem to add more inodes to the filesystem. Ahhh. I don't think I knew that resizing actually increased inode counts. Just for the experience of it, (and when I can find a moment to do it) I will probably transplant my MDT into a newly created (on LVM of course, given I do everything on LVM) device, much smaller than my current one. Indeed, I could try just shrinking the existing one, but I want to create a new one from scratch, complete with a mountconf- style UUID and move the MDT data into it. b.
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