Planet Ceph

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February 8, 2017

预估ceph的迁移数据量

cal

引言

我们在进行 ceph 的 osd 的增加和减少的维护的时候,会碰到迁移数据,但是我们平时会怎么去回答关于迁移数据量的问题,一般来说,都是说很多,或者说根据环境来看,有没有精确的一个说法,到底要迁移多少数据?这个我以前也有思考过这个问题,当时想是对比前后的pg的分布,然后进行计算,正好在翻一些资料的时候,看到有alram写的一篇博客,alram是Inktank的程序员,也就是sage所在的公司,程序是一个python脚本,本篇会分析下这个对比的思路,以及运行效果

计算迁移量只需要一个修改后的crushmap就可以了,这个是离线计算的,所以不会对集群有什么影响

运行效果

准备修改后的crushmap

获取当前crushmap

ceph osd getcrushmap -o crushmap

解码crushmap

crushtool -d crushmap -o crushmap.txt

修改crushmap.txt
这个根据自己需要,修改成自己想修改成的crushmap即可,可以是增加,也可以是删除

减少节点的计算

假如删除一个osd.5 我们需要迁移多少数据
将crushmap里面的osd.5的weight改成0

crushtool -c crushmap.txt -o crushmapnew

运行计算脚本

[root@lab8106 ceph]# python jisuan.py --crushmap-file crushmapnew
POOL REMAPPED OSDs BYTES REBALANCE OBJECTS REBALANCE
rbd 59 6157238296 1469
data 54 5918162968 1412
metadata 53 5825888280 1390

可以看到迁移的数据量
REMAPPED OSDs 下面就是有多少份的PG数据需要迁移,这里面计算的方式是比较前后的分布

[1,2] – > [1,2] 迁移0个
[1,2] – > [4,2] 迁移1个
[1,2] – > [4,3] 迁移2个

上面的统计的是这样的个数,所以不太好说是PG或者是OSD,可以理解为PG内数据的份数,因为单个PG可能需要迁移一份,也有可能迁移两份,或者多份

增加节点的计算

如果增加一个osd.6 我们需要迁移多少数据
直接运行脚本

[root@lab8106 ceph]# python jisuan.py --crushmap-file crushmapnew
POOL REMAPPED OSDs BYTES REBALANCE OBJECTS REBALANCE
rbd 0 0 0
data 0 0 0
metadata 0 0 0

可以看到没有输出,这个是因为计算的脚本里面有个地方报错了,ceph内部有个限制,在将crushmap import进osdmap的时候,ceph会验证osdmap里面的osd个数和crushmap里面的osd个数是不是相同
所以这个地方需要多做一步,将osd的个数设置成跟预估的一致,这个是唯一对现有集群做的修改操作,

[root@lab8106 ceph]# ceph osd setmaxosd 7
set new max_osd = 7

然后再次运行就可以了

[root@lab8106 ceph]# python jisuan.py --crushmap-file crushmapnew
POOL REMAPPED OSDs BYTES REBALANCE OBJECTS REBALANCE
rbd 31 3590324224 856
data 34 3372220416 804
metadata 41 4492099584 1071

上面就是运行的效果,下面我们对内部的逻辑进行分析

代码和代码分析

代码

#!/usr/bin/env python

import ast
import json
import os
import subprocess
import argparse
import sys

FNULL = open(os.devnull, 'w')

# assume the osdmap test output
# is the same lenght and order...
# if add support for PG increase
# that's gonna break
def diff_output(original, new, pools):
number_of_osd_remap = 0
osd_data_movement = 0

results = {}

pg_data, pg_objects = get_pg_info()

for i in range(len(original)):
orig_i = original[i]
new_i = new[i]

if orig_i[0].isdigit():
pg_id = orig_i.split('t')[0]
pool_id = pg_id[0]
pool_name = pools[pool_id]['pool_name']

if not pool_name in results:
results[pool_name] = {}
results[pool_name]['osd_remap_counter'] = 0
results[pool_name]['osd_bytes_movement'] = 0
results[pool_name]['osd_objects_movement'] = 0

original_mappings = ast.literal_eval(orig_i.split('t')[1])
new_mappings = ast.literal_eval(new_i.split('t')[1])
intersection = list(set(original_mappings).intersection(set(new_mappings)))

osd_movement_for_this_pg = int(pools[pool_id]['pool_size']) - len(intersection)
osd_data_movement_for_this_pg = int(osd_movement_for_this_pg) * int(pg_data[pg_id])
osd_object_movement_for_this_pg = int(osd_movement_for_this_pg) * int(pg_objects[pg_id])

results[pool_name]['osd_remap_counter'] += osd_movement_for_this_pg
results[pool_name]['osd_bytes_movement'] += int(osd_data_movement_for_this_pg)
results[pool_name]['osd_objects_movement'] += int(osd_object_movement_for_this_pg)

elif orig_i.startswith('#osd'):
break

return results

def get_pools_info(osdmap_path):
pools = {}
args = ['osdmaptool', '--print', osdmap_path]
osdmap_out = subprocess.check_output(args, stderr=FNULL).split('n')
for line in osdmap_out:
if line.startswith('pool'):
pool_id = line.split()[1]
pool_size = line.split()[5]
pool_name = line.split()[2].replace("'","")
pools[pool_id] = {}
pools[pool_id]['pool_size'] = pool_size
pools[pool_id]['pool_name'] = pool_name
elif line.startswith('max_osd'):
break

return pools

def get_osd_map(osdmap_path):
args = ['sudo', 'ceph', 'osd', 'getmap', '-o', osdmap_path]
subprocess.call(args, stdout=FNULL, stderr=subprocess.STDOUT)

def get_pg_info():
pg_data = {}
pg_objects = {}
args = ['sudo', 'ceph', 'pg', 'dump']
pgmap = subprocess.check_output(args, stderr=FNULL).split('n')

for line in pgmap:
if line[0].isdigit():
pg_id = line.split('t')[0]
pg_bytes = line.split('t')[6]
pg_obj = line.split('t')[1]
pg_data[pg_id] = pg_bytes
pg_objects[pg_id] = pg_obj
elif line.startswith('pool'):
break

return pg_data, pg_objects

def osdmaptool_test_map_pgs_dump(original_osdmap_path, crushmap):
new_osdmap_path = original_osdmap_path + '.new'
get_osd_map(original_osdmap_path)
args = ['osdmaptool', '--test-map-pgs-dump', original_osdmap_path]
original_osdmaptool_output = subprocess.check_output(args, stderr=FNULL).split('n')

args = ['cp', original_osdmap_path, new_osdmap_path]
subprocess.call(args, stdout=FNULL, stderr=subprocess.STDOUT)
args = ['osdmaptool', '--import-crush', crushmap, new_osdmap_path]
subprocess.call(args, stdout=FNULL, stderr=subprocess.STDOUT)
args = ['osdmaptool', '--test-map-pgs-dump', new_osdmap_path]
new_osdmaptool_output = subprocess.check_output(args, stderr=FNULL).split('n')

pools = get_pools_info(original_osdmap_path)
results = diff_output(original_osdmaptool_output, new_osdmaptool_output, pools)

return results


def dump_plain_output(results):
sys.stdout.write("%-20s %-20s %-20s %-20sn" % ("POOL", "REMAPPED OSDs", "BYTES REBALANCE", "OBJECTS REBALANCE"))

for pool in results:
sys.stdout.write("%-20s %-20s %-20s %-20sn" % (
pool,
results[pool]['osd_remap_counter'],
results[pool]['osd_bytes_movement'],
results[pool]['osd_objects_movement']
))

def cleanup(osdmap):
FNULL.close()
new_osdmap = osdmap + '.new'
os.remove(new_osdmap)

def parse_args():
parser = argparse.ArgumentParser(description='Ceph CRUSH change data movement calculator.')

parser.add_argument(
'--osdmap-file',
help="Where to save the original osdmap. Temp one will be <location>.new. Default: /tmp/osdmap",
default="/tmp/osdmap",
dest="osdmap_path"
)
parser.add_argument(
'--crushmap-file',
help="CRUSHmap to run the movement test against.",
required=True,
dest="new_crushmap"
)

parser.add_argument(
'--format',
help="Output format. Default: plain",
choices=['json', 'plain'],
dest="format",
default="plain"
)

args = parser.parse_args()
return args

if __name__ == '__main__':
ctx = parse_args()

results = osdmaptool_test_map_pgs_dump(ctx.osdmap_path, ctx.new_crushmap)
cleanup(ctx.osdmap_path)

if ctx.format == 'json':
print json.dumps(results)
elif ctx.format == 'plain':
dump_plain_output(results)

直接放在这里方便拷贝,也可以去原作者的gist里面去获取

主要代码分析

首先获取osdmap

ceph osd getmap -o /tmp/osdmap

获取原始pg分布

使用osdmaptool  --test-map-pgs-dump /tmp/osdmap

获取新的crushmap

这个是自己编辑成需要的crushmap

将新的crushmap注入到osdmap里面得到新的osdmap

osdmaptool --import-crush  crushmap  /tmp/new_osdmap_path

根据新的osdmap进行计算新的分布

osdmaptool  --test-map-pgs-dump /tmp/new_osdmap_path

然后比较两个输入进行对比得到结果

相关链接

Calculate data migration when changing the CRUSHmap
alram/crush_data_movement_calculator.py

变更记录

Why Who When
创建 武汉-运维-磨渣 2017-02-08

Source: zphj1987@gmail (预估ceph的迁移数据量)

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