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Added post about Synology reshape.
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know-how/hardware/_posts/2017-05-28-speed-up-synology-reshape.md
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know-how/hardware/_posts/2017-05-28-speed-up-synology-reshape.md
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---
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title: Speed up Synology volume reshaping
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layout: default
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language: en
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created: 2017-05-28 23:45:40 +0200
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updated: 2017-05-28 23:45:40 +0200
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toc: false
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tags:
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- know-how
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- hardware
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- synology
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- diskstation
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- dsm
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- raid
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- lvm
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- reshape
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- storage
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---
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I wanted to increase the available storage on my Synology DS415+ by replacing 2x 2TB disks with
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4TB ones, changing my 4-4-2-2 configuration to 4-4-4-4 and the overall storage space from 8TB to
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12TB.
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After replacing the first disk, there was the data reconstruction which finished after 2 hours
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or so. But then came the reshaping which I left running over night (~10 hours) and it still only
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got to 20%.
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That made me wonder how long the overall process might take and if that is normal.
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Google brought me to [this](https://forum.synology.com/enu/viewtopic.php?t=79595) and
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[this](https://forum.synology.com/enu/viewtopic.php?t=124489) forum post which suggested this
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command for checking the status and estimated runtime:
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```
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root@DiskStation:~# cat /proc/mdstat
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Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
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md3 : active raid5 sdd6[2] sda6[0] sdb6[1]
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1953494784 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/3] [UUU]
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[=====>...............] reshape = 25.1% (491263360/1953494784) finish=5198.4min speed=4687K/sec
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md2 : active raid5 sdd5[4] sda5[0] sdc5[5] sdb5[1]
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5846049792 blocks super 1.2 level 5, 64k chunk, algorithm 2 [4/4] [UUUU]
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md1 : active raid1 sdd2[3] sda2[0] sdb2[1] sdc2[2]
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2097088 blocks [4/4] [UUUU]
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md0 : active raid1 sdd1[3] sda1[0] sdb1[1] sdc1[2]
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2490176 blocks [4/4] [UUUU]
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unused devices: <none>
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```
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As you can see, for me it showed about 5200 minutes left. That would be almost 87 hours, or a
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little bit over 3½ days. Given that some people reported runtimes of 16 days, I assumed I was
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lucky already.
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However, the `speed` indicator of the above command showed values around 4-6 MB/sec which is
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rather slow for hard drives capable of 100 MB/sec and more.
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People mentioned running services on the DiskStation to be a problem, especially indexing services
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for e.g. the PhotoStation. So I stopped every service I didn't need (from the *Package Manager*)
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and paused those services which appeared at the top for the `top` command, i.e. which were using
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the CPU:
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```
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root@DiskStation:~# synoservice --pause synomkthumbd
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root@DiskStation:~# synoservice --pause pkgctl-FileStation
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root@DiskStation:~# synoservice --pause scemd
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root@DiskStation:~# synoservice --pause synorelayd
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root@DiskStation:~# synoservice --pause synoindexd
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```
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(Just remember to `--resume` them after everything is done.)
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Now to the tweaking of the lvm parameters. Since I didn't want to just change settings to values
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from the forums without knowing why and what they do, I searched for a site explaining the
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different parameters and I found [this nice page](https://baptiste-wicht.com/posts/2015/03/how-to-speed-up-raid-5-6-growing-with-mdadm.html)
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which explains the commands and their effects in terms of speed and memory consumption.
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The `sysctl dev.raid.speed_limit_max` already showed a reasonable value of `200000` (200 MB/sec)
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but I raised it to 500 MB/sec - just to be sure.
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sysctl -w dev.raid.speed_limit_max=500000
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As expected, this didn't do anything. On to the next parameter from that page - the
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`stripe_cache_size`. First, check the current (default) value:
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root@DiskStation:~# cat /sys/block/md3/md/stripe_cache_size
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256
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This means the stripe cache is 256 pages of 4096 Bytes each = 1 MiB per disk. Not very much.
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So I increased it as per the recommendation to 4096 pages = 16 MiB per disk:
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echo 4096 > /sys/block/md2/md/stripe_cache_size
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echo 4096 > /sys/block/md3/md/stripe_cache_size
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(`md2` and `md3` are my `raid5` devices. See `mdstat` output above.)
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This brought the biggest effect. The estimated runtime left immediately fell to around 1300
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minutes, fluctuating between 1100 and 1800 minutes:
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```
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root@DiskStation:~# cat /proc/mdstat
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Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
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md3 : active raid5 sdd6[2] sda6[0] sdb6[1]
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1953494784 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/3] [UUU]
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[=====>...............] reshape = 26.0% (509001728/1953494784) finish=1338.0min speed=17992K/sec
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```
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That was already impressive, cutting down the overall time from 3.5 days to 22 hours.
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And we had another parameter to tweak: the read-ahead. Again, we first want to figure out the
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default value:
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root@DiskStation:~# blockdev --getra /dev/md3
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384
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Since the value is in "sectors" of 512 Bytes, that comes in at 192 KiB. As we have plenty of RAM
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(upgraded my DS to 8GB), I've set this to the recommended 32 MiB:
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root@DiskStation:~# blockdev --setra 65536 /dev/md3
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root@DiskStation:~# blockdev --setra 65536 /dev/md2
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And that gave another small boost:
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```
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root@DiskStation:~# cat /proc/mdstat
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Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
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md3 : active raid5 sdd6[2] sda6[0] sdb6[1]
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1953494784 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/3] [UUU]
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[=====>...............] reshape = 26.1% (511295616/1953494784) finish=1001.1min speed=24008K/sec
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```
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Another 300 minutes (5 hours) shaved off the remaining time. With a remaining time of less
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than 17 hours for something which initially needed 3.5 days, I was very pleased.
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And the process seems to have sped up even more as it is now - 9.5 hours later - nearing completion:
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```
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root@DiskStation:~# cat /proc/mdstat
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Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
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md3 : active raid5 sdd6[2] sda6[0] sdb6[1]
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1953494784 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/3] [UUU]
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[===================>.] reshape = 95.9% (1874314432/1953494784) finish=20.1min speed=65521K/sec
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```
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*[MiB]: Mebibyte (1024 KiB), similar to Megabyte (1000 kB)
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*[KiB]: Kibibyte (1024 Bytes), similar to Kilobyte (1000 Bytes)
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