Search found 420 matches

by chemal
2018/09/25 13:57:23
Forum: CentOS 7 - General Support
Topic: CentOS slows down when copying large files
Replies: 21
Views: 2057

Re: CentOS slows down when copying large files

Kyber is for mq-blk only. You either need an NVME SSD or you can try the scsi_mod.use_blk_mq=y technology preview option.

https://access.redhat.com/documentation ... es/storage
by chemal
2018/09/24 16:27:50
Forum: CentOS 7 - General Support
Topic: CentOS slows down when copying large files
Replies: 21
Views: 2057

Re: CentOS slows down when copying large files

Some additional tests with an NVME SSD (Samsung SM961). NVME SSDs have multiple hardware submission queues and RH has backported multiqueue I/O scheduling. So even with the default 'none' scheduler, the background writes do not monopolize the SSD. Oowriter starts in parallel to heavy dd-ing. But the...
by chemal
2018/09/24 13:57:34
Forum: CentOS 7 - General Support
Topic: CentOS slows down when copying large files
Replies: 21
Views: 2057

Re: CentOS slows down when copying large files

For consumer-grade SATA SSDs, CFQ is ok. It has SSD optimizations (see kernel docs). And it's the only way to solve problem #2 (background writes hog drive) with the distro kernel as far as I can see.
by chemal
2018/09/24 01:37:37
Forum: CentOS 7 - General Support
Topic: CentOS slows down when copying large files
Replies: 21
Views: 2057

Re: CentOS slows down when copying large files

# don't buffer too many writes echo $((16*1024*1024)) > /proc/sys/vm/dirty_background_bytes echo $((48*1024*1024)) > /proc/sys/vm/dirty_bytes # enable completely fair queuing echo cfq > /sys/block/sda/queue/scheduler Adding CFQ on top seems to solve both problems. I no longer have to wait until dd ...
by chemal
2018/09/22 23:17:07
Forum: CentOS 7 - General Support
Topic: CentOS slows down when copying large files
Replies: 21
Views: 2057

Re: CentOS slows down when copying large files

A nice test is mentioned there. Type dd if=/dev/zero of=foo bs=1M count=10k in one terminal and start some large program (not used since last reboot, it must come frome disk) in another, e.g. oowriter It will not pop up on my CentOS 7 machine until dd is through. Seems I'm not doing this normally. :...
by chemal
2018/09/22 20:36:53
Forum: CentOS 7 - General Support
Topic: CentOS slows down when copying large files
Replies: 21
Views: 2057

Re: CentOS slows down when copying large files

I'm not sure what "copying issue" you are refering to and heard is fixed in later kernels. I've never heard of this. What Linux does here is a feature not a bug. It buffers writes and then does them asynchronously to improve performance. Only problem is that per default a lot of writes are buffered ...
by chemal
2018/09/22 18:20:00
Forum: CentOS 7 - General Support
Topic: CentOS slows down when copying large files
Replies: 21
Views: 2057

Re: CentOS slows down when copying large files

Try this: # don't buffer too many writes echo $((16*1024*1024)) > /proc/sys/vm/dirty_background_bytes echo $((48*1024*1024)) > /proc/sys/vm/dirty_bytes It means: start writing out when you have accumulated 16M of dirty buffers and stop buffering more writes if there are 48M of dirty buffers. This wa...
by chemal
2018/08/28 04:44:59
Forum: CentOS 6 - Software Support
Topic: run a c++ program with c++11 support in older CentOS machine
Replies: 3
Views: 517

Re: run a c++ program with c++11 support in older CentOS machine

Now I have to run my program on CentOS 6.10 for production.
Compile your source code on 6.10. You can choose from five devtoolsets offering gcc 4.8.2, 4.9.2, 5.3.1, 6.3.1, and 7.3.1, respectively. That should be enough C++11.
by chemal
2018/08/12 22:52:03
Forum: CentOS 7 - Hardware Support
Topic: Installing Centos 7 on Samsung 850 Pro
Replies: 1
Views: 382

Re: Installing Centos 7 on Samsung 850 Pro

The 850 Pro is a standard SATA drive. If it is properly connected and not detected by Linux, it's broken.