[Gluster-users] Gluster linear scale-out performance

Artem Russakovskii archon810 at gmail.com
Fri Jul 24 23:05:10 UTC 2020

Speaking of fio, could the gluster team please help me understand something?

We've been having lots of performance issues related to gluster using
attached block storage on Linode. At some point, I figured out that Linode
has a cap of 500 IOPS on their block storage
(with spikes to 1500 IOPS). The block storage we use is formatted xfs with
4KB bsize (block size).

I then ran a bunch of fio tests on the block storage itself (not the
gluster fuse mount), which performed horribly when the bs parameter was set
to 4k:
fio --randrepeat=1 --ioengine=libaio --direct=1 --gtod_reduce=1 --name=test
--filename=test --bs=4k --iodepth=64 --size=4G --readwrite=randwrite
During these tests, fio ETA crawled to over an hour, at some point dropped
to 45min and I did see 500-1500 IOPS flash by briefly, then it went back
down to 0. I/O seems majorly choked for some reason, likely because gluster
is using some of it. Transfer speed with such 4k block size is 2 MB/s with
spikes to 6MB/s. This causes the load on the server to spike up to 100+ and
brings down all our servers.

Jobs: 1 (f=1): [w(1)][20.3%][r=0KiB/s,w=5908KiB/s][r=0,w=1477
IOPS][eta 43m:00s]    Jobs: 1 (f=1):
[w(1)][21.5%][r=0KiB/s,w=0KiB/s][r=0,w=0 IOPS][eta 44m:54s]

xfs_info /mnt/citadel_block1
meta-data=/dev/sdc               isize=512    agcount=103, agsize=26214400 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=1, sparse=0, rmapbt=0
         =                       reflink=0
data     =                       bsize=4096   blocks=2684354560, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0, ftype=1log
   =internal log           bsize=4096   blocks=51200, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

When I increase the --bs param to fio from 4k to, say, 64k, transfer speed
goes up significantly and is more like 50MB/s, and at 256k, it's 200MB/s.

So what I'm trying to understand is:

   1. How does the xfs block size (4KB) relate to the block size in fio
   tests? If we're limited by IOPS, and xfs block size is 4KB, how can fio
   produce better results with varying --bs param?
   2. Would increasing the xfs data block size to something like 64-256KB
   help with our issue of choking IO and skyrocketing load?
   3. The worst hangs and load spikes happen when we reboot one of the
   gluster servers, but not when it's down - when it comes back online. Even
   with gluster not showing anything pending heal, my guess is it's still
   trying to do lots of IO between the 4 nodes for some reason, but I don't
   understand why.

I've been banging my head on the wall with this problem for months.
Appreciate any feedback here.

Thank you.

gluster volume info below

Volume Name: SNIP_data1
Type: Replicate
Volume ID: SNIP
Status: Started
Snapshot Count: 0
Number of Bricks: 1 x 4 = 4
Transport-type: tcp
Brick1: nexus2:/mnt/SNIP_block1/SNIP_data1
Brick2: forge:/mnt/SNIP_block1/SNIP_data1
Brick3: hive:/mnt/SNIP_block1/SNIP_data1
Brick4: citadel:/mnt/SNIP_block1/SNIP_data1
Options Reconfigured:
cluster.quorum-count: 1
cluster.quorum-type: fixed
network.ping-timeout: 5
network.remote-dio: enable
performance.rda-cache-limit: 256MB
performance.readdir-ahead: on
performance.parallel-readdir: on
network.inode-lru-limit: 500000
performance.md-cache-timeout: 600
performance.cache-invalidation: on
performance.stat-prefetch: on
features.cache-invalidation-timeout: 600
features.cache-invalidation: on
cluster.readdir-optimize: on
performance.io-thread-count: 32
server.event-threads: 4
client.event-threads: 4
performance.read-ahead: off
cluster.lookup-optimize: on
performance.cache-size: 1GB
cluster.self-heal-daemon: enable
transport.address-family: inet
nfs.disable: on
performance.client-io-threads: on
cluster.granular-entry-heal: enable
cluster.data-self-heal-algorithm: full


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On Thu, Jul 23, 2020 at 12:08 AM Qing Wang <qw at g.clemson.edu> wrote:

> Hi,
> I have one more question about the Gluster linear scale-out performance
> regarding the "write-behind off" case specifically -- when "write-behind"
> is off, and still the stripe volumes and other settings as early thread
> posted, the storage I/O seems not to relate to the number of storage
> nodes. In my experiment, no matter I have 2 brick server nodes or 8 brick
> server nodes, the aggregated gluster I/O performance is ~100MB/sec. And fio
> benchmark measurement gives the same result. If "write behind" is on, then
> the storage performance is linear scale-out along with the # of brick
> server nodes increasing.
> No matter the write behind option is on/off, I thought the gluster I/O
> performance should be pulled and aggregated together as a whole. If that is
> the case, why do I get a consistent gluster performance (~100MB/sec) when
> "write behind" is off? Please advise me if I misunderstood something.
> Thanks,
> Qing
> On Tue, Jul 21, 2020 at 7:29 PM Qing Wang <qw at g.clemson.edu> wrote:
>> fio gives me the correct linear scale-out results, and you're right, the
>> storage cache is the root cause that makes the dd measurement results not
>> accurate at all.
>> Thanks,
>> Qing
>> On Tue, Jul 21, 2020 at 2:53 PM Yaniv Kaul <ykaul at redhat.com> wrote:
>>> On Tue, 21 Jul 2020, 21:43 Qing Wang <qw at g.clemson.edu> wrote:
>>>> Hi Yaniv,
>>>> Thanks for the quick response. I forget to mention I am testing the
>>>> writing performance, not reading. In this case, would the client cache hit
>>>> rate still be a big issue?
>>> It's not hitting the storage directly. Since it's also single threaded,
>>> it may also not saturate it. I highly recommend testing properly.
>>> Y.
>>>> I'll use fio to run my test once again, thanks for the suggestion.
>>>> Thanks,
>>>> Qing
>>>> On Tue, Jul 21, 2020 at 2:38 PM Yaniv Kaul <ykaul at redhat.com> wrote:
>>>>> On Tue, 21 Jul 2020, 21:30 Qing Wang <qw at g.clemson.edu> wrote:
>>>>>> Hi,
>>>>>> I am trying to test Gluster linear scale-out performance by adding
>>>>>> more storage server/bricks, and measure the storage I/O performance. To
>>>>>> vary the storage server number, I create several "stripe" volumes that
>>>>>> contain 2 brick servers, 3 brick servers, 4 brick servers, and so on. On
>>>>>> gluster client side, I used "dd if=/dev/zero
>>>>>> of=/mnt/glusterfs/dns_test_data_26g bs=1M count=26000" to create 26G data
>>>>>> (or larger size), and those data will be distributed to the corresponding
>>>>>> gluster servers (each has gluster brick on it) and "dd" returns the final
>>>>>> I/O throughput. The Internet is 40G infiniband, although I didn't do any
>>>>>> specific configurations to use advanced features.
>>>>> Your dd command is inaccurate, as it'll hit the client cache. It is
>>>>> also single threaded. I suggest switching to fio.
>>>>> Y.
>>>>>> What confuses me is that the storage I/O seems not to relate to the
>>>>>> number of storage nodes, but Gluster documents said it should be linear
>>>>>> scaling. For example, when "write-behind" is on, and when Infiniband "jumbo
>>>>>> frame" (connected mode) is on, I can get ~800 MB/sec reported by "dd", no
>>>>>> matter I have 2 brick servers or 8 brick servers -- for 2 server case, each
>>>>>> server can have ~400 MB/sec; for 4 server case, each server can have
>>>>>> ~200MB/sec. That said, each server I/O does aggregate to the final storage
>>>>>> I/O (800 MB/sec), but this is not "linear scale-out".
>>>>>> Can somebody help me to understand why this is the case? I certainly
>>>>>> can have some misunderstanding/misconfiguration here. Please correct me if
>>>>>> I do, thanks!
>>>>>> Best,
>>>>>> Qing
>>>>>> ________
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>>>>> ________
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