<div dir="ltr"><div><div>Hi, </div>I'm a newbie to dm, and i'm not sure if it's the right place to ask the following question. Please correct me if not, and thanks for any reply. </div><div>In short, I did mkfs.ext3 on a dm thin-vol, and it looks consumed much more data space than on a loop image. As a result, mkfs failed due to inadequate space. --- [root@vm ~]# dd if=/dev/zero of=10G_1.img bs=1 count=0 seek=10G 0+0 records in 0+0 records out 0 bytes (0 B) copied, 0.000102011 s, 0.0 kB/s [root@vm ~]# /usr/sbin/mkfs -t ext3 -- -F -b 1024 10G_1.img mke2fs 1.42.9 (28-Dec-2013) Discarding device blocks: done Filesystem label= OS type: Linux Block size=1024 (log=0) Fragment size=1024 (log=0) Stride=0 blocks, Stripe width=0 blocks 655360 inodes, 10485760 blocks 524288 blocks (5.00%) reserved for the super user First data block=1 Maximum filesystem blocks=77594624 1280 block groups 8192 blocks per group, 8192 fragments per group 512 inodes per group Superblock backups stored on blocks: 8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409, 663553, 1024001, 1990657, 2809857, 5120001, 5971969 Allocating group tables: done Writing inode tables: done Creating journal (32768 blocks): done Writing superblocks and filesystem accounting information: done [root@vm ~]# du -sh 10G_1.img 199M 10G_1.img --- </div><div>As shown above, mks.ext3 on a 10G loop image should use 199M space. In the following test, i'll create a dm thin-vol with 10G virtual size and 500m backing size, and i expect 500m is adequate for mkfs.ext3. --- [root@vm ~]# dd if=/dev/zero of=10G.img bs=1 count=0 seek=10G 0+0 records in 0+0 records out 0 bytes (0 B) copied, 0.000125097 s, 0.0 kB/s [root@vm ~]# losetup /dev/loop0 /root/10G.img [root@vm ~]# /usr/sbin/dmsetup create thin-meta --table '0 48000 linear /dev/loop0 10240' [root@vm ~]# /usr/sbin/dmsetup create thin-data --table '0 1024000 linear /dev/loop0 58240' [root@vm ~]# /usr/sbin/dmsetup create thin-pool --table '0 1024000 thin-pool /dev/mapper/thin-meta /dev/mapper/thin-data 1024 200' [root@vm ~]# /usr/sbin/dmsetup message /dev/mapper/thin-pool 0 'create_thin 17021' [root@vm ~]# /usr/sbin/dmsetup create thin-vol --table '0 10240000 thin /dev/mapper/thin-pool 17021' [root@vm ~]# dmsetup status | grep pool thin-pool: 0 1024000 thin-pool 0 10/6000 0/1000 - rw discard_passdown queue_if_no_space - [root@vm ~]# /usr/sbin/mkfs -t ext3 -- -F -b 1024 /dev/mapper/thin-vol mke2fs 1.42.9 (28-Dec-2013) Discarding device blocks: done Filesystem label= OS type: Linux Block size=1024 (log=0) Fragment size=1024 (log=0) Stride=64 blocks, Stripe width=512 blocks 320000 inodes, 5120000 blocks 256000 blocks (5.00%) reserved for the super user First data block=1 Maximum filesystem blocks=72351744 625 block groups 8192 blocks per group, 8192 fragments per group 512 inodes per group Superblock backups stored on blocks: 8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409, 663553, 1024001, 1990657, 2809857 Allocating group tables: done Writing inode tables: done Creating journal (32768 blocks): done Writing superblocks and filesystem accounting information: Warning, had trouble writing out superblocks. [root@vm ~]# echo $? 5 [root@vm ~]# dmsetup status | grep pool thin-pool: 0 1024000 thin-pool 0 17/6000 1000/1000 - out_of_data_space discard_passdown error_if_no_space - [root@vm ~]# journalctl -k Jan 15 18:15:38 vm kernel: device-mapper: thin: 253:8: switching pool to write mode Jan 15 18:15:38 vm kernel: device-mapper: thin: 253:8: switching pool to out-of-data-space (queue IO) mode Jan 15 18:16:39 vm kernel: device-mapper: thin: 253:8: switching pool to out-of-data-space (error IO) mode Jan 15 18:16:39 vm kernel: buffer_io_error: 25590 callbacks suppressed Jan 15 18:16:39 vm kernel: Buffer I/O error on dev dm-9, logical block 988832, lost async page write Jan 15 18:16:39 vm kernel: Buffer I/O error on dev dm-9, logical block 989184, lost async page write Jan 15 18:16:39 vm kernel: Buffer I/O error on dev dm-9, logical block 990896, lost async page write Jan 15 18:16:39 vm kernel: Buffer I/O error on dev dm-9, logical block 991232, lost async page write Jan 15 18:16:39 vm kernel: Buffer I/O error on dev dm-9, logical block 992960, lost async page write Jan 15 18:16:39 vm kernel: Buffer I/O error on dev dm-9, logical block 993280, lost async page write Jan 15 18:16:39 vm kernel: Buffer I/O error on dev dm-9, logical block 995024, lost async page write Jan 15 18:16:39 vm kernel: Buffer I/O error on dev dm-9, logical block 995328, lost async page write Jan 15 18:16:39 vm kernel: Buffer I/O error on dev dm-9, logical block 997088, lost async page write Jan 15 18:16:39 vm kernel: Buffer I/O error on dev dm-9, logical block 997376, lost async page write --- </div><div>In another test, mkfs succeeds with creating a 2500m virtual size thin-vol instead of 5000m: /usr/sbin/dmsetup create thin-vol --table '0 5120000 thin /dev/mapper/thin-pool 17021' </div><div>I think the failure is due to mkfs runs out of space on dm thin-vol, but why is it? </div><div>Thanks, </div><div>Young </div><div> </div></div>