MdadmLVMext4

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Preliminaries

For faster rebuild 

# echo "dev.raid.speed_limit_min=100000 # set higher raid rebuild limit" >> /etc/sysctl.conf

For Faster Writes Add this to a script on boot ( rc.local ) 

# echo 16384 > /sys/block/md127/md/stripe_cache_size

Beware of RAM usage: Value in pages per device, i.e. on 4 devices at 8192 comes out to 128MB

After enabling SATA AHCI in BIOS! 

[root@drewserv ~]# dd if=/dev/md127 of=/dev/null bs=4M count=2500
2500+0 records in
2500+0 records out
10485760000 bytes (10 GB) copied, 57.1676 s, 183 MB/s


Build the array

# mdadm -v --create /dev/md127 -l 5 -c 512 --bitmap=internal --raid-devices=3 /dev/sdb /dev/sdd /dev/sde
-------------------------------------------------------------------------------------------
[root@drewserv ~]# mdadm -D /dev/md127
/dev/md127:
        Version : 1.2
  Creation Time : Fri Jul 22 22:24:38 2011
     Raid Level : raid5
     Array Size : 976770048 (931.52 GiB 1000.21 GB)
  Used Dev Size : 488385024 (465.76 GiB 500.11 GB)
   Raid Devices : 3
  Total Devices : 3
    Persistence : Superblock is persistent

  Intent Bitmap : Internal

    Update Time : Sat Jul 23 00:25:31 2011
          State : active
 Active Devices : 3
Working Devices : 3
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 512K

           Name : 127
           UUID : e9355597:7a4ff30b:21b71007:42443f63
         Events : 21

    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       1       8       48        1      active sync   /dev/sdd
       3       8       64        2      active sync   /dev/sde

MD RAID5 Perf Tests

[root@drewserv ~]# dd if=/dev/md127 of=/dev/null count=10000 bs=1M
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 63.5414 s, 165 MB/s

Write Test
[root@drewserv ~]# cat /sys/block/md127/md/stripe_cache_size 
256
[root@drewserv ~]# echo 16384 > /sys/block/md127/md/stripe_cache_size 
[root@drewserv ~]# cat /sys/block/md127/md/stripe_cache_size 
16384
[root@drewserv ~]# dd if=/dev/zero of=/dev/md127 count=10000 bs=1M
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 74.9109 s, 140 MB/s


Create LVM VG/PV/LV

[root@drewserv ~]# vgcreate vg-raid5 /dev/md127
  No physical volume label read from /dev/md127
  Physical volume "/dev/md127" successfully created
  Volume group "vg-raid5" successfully created
[root@drewserv ~]# vgdisplay -v vg-raid5
    Using volume group(s) on command line
    Finding volume group "vg-raid5"
  --- Volume group ---
  VG Name               vg-raid5
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  1
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                0
  Open LV               0
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               931.52 GiB
  PE Size               4.00 MiB
  Total PE              238469
  Alloc PE / Size       0 / 0   
  Free  PE / Size       238469 / 931.52 GiB
  VG UUID               MbPYwg-Q12h-YoEq-oh1p-dlKH-HwaP-fiKRzq
   
  --- Physical volumes ---
  PV Name               /dev/md127     
  PV UUID               eeErmO-wm0Z-p870-6uJp-TcMJ-tgSm-NAq1BX
  PV Status             allocatable
  Total PE / Free PE    238469 / 238469
   

root@drewserv ~]# lvcreate -l 178850 -n lv-raid5 vg-raid5
  Logical volume "lv-raid5" created

root@drewserv ~]# lvdisplay /dev/vg-raid5/lv-raid5 
  --- Logical volume ---
  LV Name                /dev/vg-raid5/lv-raid5
  VG Name                vg-raid5
  LV UUID                QYuPPT-TqzR-bDC5-6Cjd-DYDj-W102-0oK4Or
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                698.63 GiB
  Current LE             178850
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     4096
  Block device           253:4

LVM Performance Tests

[root@drewserv ~]# dd if=/dev/vg-raid5/lv-raid5 of=/dev/null count=10000 bs=1M
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 67.0551 s, 156 MB/s

[root@drewserv ~]# dd if=/dev/zero of=/dev/md127 count=10000 bs=1M
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 71.3196 s, 147 MB/s

Create the filesystem (EXT4)

  • Dry run for fs*
[root@drewserv ~]# mkfs.ext4 -v -E stride=128 -E stripe-width=256 -m 0 -n /dev/vg-raid5/lv-raid5 
mke2fs 1.41.14 (22-Dec-2010)
fs_types for mke2fs.conf resolution: 'ext4'
Calling BLKDISCARD from 0 to 750151270400 failed.
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=128 blocks, Stripe width=256 blocks
45793280 inodes, 183142400 blocks
0 blocks (0.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=4294967296
5590 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks: 
	32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
	4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968, 
	102400000

Real run 

[root@drewserv ~]# mkfs.ext4 -v -E stride=128 -E stripe-width=256 -m 0 /dev/vg-raid5/lv-raid5 
mke2fs 1.41.14 (22-Dec-2010)
fs_types for mke2fs.conf resolution: 'ext4'
Calling BLKDISCARD from 0 to 750151270400 failed.
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=128 blocks, Stripe width=256 blocks
45793280 inodes, 183142400 blocks
0 blocks (0.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=4294967296
5590 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks: 
	32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
	4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968, 
	102400000

Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 34 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

Filesystem Performance Tests

Write test 

[root@drewserv raid5]# dd if=/dev/zero of=/mnt/raid5/10Gtest count=10000 bs=1M
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 73.8108 s, 142 MB/s

Read Test 

[root@drewserv raid5]# dd if=/mnt/raid5/10Gtest of=/dev/null count=10000 bs=1M
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 85.8405 s, 122 MB/s

test2 after rebuild
[drew@drewserv raid5]$ sudo dd if=/dev/zero of=/mnt/raid5/10Gtest bs=1M count=10000
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 126.455 s, 82.9 MB/s
[drew@drewserv raid5]$ sudo dd if=/mnt/raid5/10Gtest of=/dev/null bs=1M count=10000
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 76.3866 s, 137 MB/s

Add to /etc/fstab

# blkid | grep raid5
/dev/mapper/vg--raid5-lv--raid5: UUID="16bf772d-bd34-4a14-b314-cea1ed737040" TYPE="ext4" 

# echo "UUID="16bf772d-bd34-4a14-b314-cea1ed737040" /mnt/raid5 ext4 defaults  1 3" >> /etc/fstab

Restore data from backup

Copy data back: 

[root@drewserv ~]# rsync -aqv --log-file=/root/bkup-raid5 /mnt/backup/backup/ /mnt/raid5/
2011/07/23 17:28:17 [8373] building file list
2011/07/23 17:28:17 [8373] .d..t...... ./
.
.
.
2011/07/23 21:49:09 [8373] .d..t...... lost+found/
2011/07/23 21:49:09 [8373] sent 428464277809 bytes  received 1589811 bytes  27373637.92 bytes/sec
2011/07/23 21:49:09 [8373] total size is 428406181021  speedup is 1.00



NOTES NOTES NOTES

http://en.wikipedia.org/wiki/Mdadm http://www.mythtv.org/wiki/LVM_on_RAID#Performance_Enhancements_.2F_Tuning

Increasing RAID5 Performance To help RAID5 read/write performance, setting the read-ahead & stripe cache size[2] [3] for the array provides noticeable speed improvements. Note: This tip assumes sufficient RAM availability to the system. Insufficient RAM can lead to data loss/corruption

sets strip cache----

  1. echo 16384 > /sys/block/md127/md/stripe_cache_size

^----- Value in pages per device, i.e. on 4 devices at 8192 comes out to 128MB

Sets read-ahead---- / try 32768 , 65536 , 131072 , 262144

  1. blockdev --setra 16384 /dev/md127
  2. blockdev --setra 16384 /dev/video_vg/video_lv
  1. blockdev --setra 16384 /dev/sdb
  2. blockdev --setra 16384 /dev/sdd
  3. blockdev --setra 16384 /dev/sde


///////////////////////////////////////???????????????????

  1. Options used:
  2. blockdev --setra 1536 /dev/md3 (back to default)
  3. cat /sys/block/sd{e,g,i,k}/queue/max_sectors_kb
  4. value: 512
  5. value: 512
  6. value: 512
  7. value: 512
  8. Test with, chunksize of raid array (128)
  9. echo 128 > /sys/block/sde/queue/max_sectors_kb
  10. echo 128 > /sys/block/sdg/queue/max_sectors_kb
  11. echo 128 > /sys/block/sdi/queue/max_sectors_kb
  12. echo 128 > /sys/block/sdk/queue/max_sectors_kb


http://www.pcguide.com/ref/hdd/perf/raid/concepts/perfStripe-c.html http://wiki.centos.org/HowTos/Disk_Optimization For example if you have 4 drives in RAID5 and it is using 64K chunks and given a 4K file system block size. The stride size is calculated for the one disk by (chunk size / block size), (64K/4K) which gives 16. While the stripe width for RAID5 is 1 disk less, so we have 3 data-bearing disks out of the 4 in this RAID5 group, which gives us (number of data-bearing drives * stride size), (3*16) gives you a stripe width of 48.

When you create an ext3 partition in this manner, you would format it like this

mkfs.ext3 -b 4096 -E stride=16 -E stripe-width=48 -O dir_index /dev/XXXX

http://www.nickyeates.com/technology/unix/raid_filesystem_lvm Note: You would want to change the stride-width if you added disks to array. 

   tune2fs -E stride=n,stripe-width=m /dev/mdx
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