158
votes
Accepted
Software vs hardware RAID performance and cache usage
In short: if using a low-end RAID card (without cache), do yourself a favor and switch to software RAID. If using a mid-to-high-end card (with BBU or NVRAM), then hardware is often (but not always! ...
- 45.5k
68
votes
Accepted
Should I be concerned that swap is being used on a host with nearly 40GB of free memory?
This is not a problem and is likely normal. Lots of code (and possibly data) is used very rarely so the system will swap it out to free up memory.
Swapping is mostly only a problem if memory is being ...
- 115k
65
votes
Accepted
bzip2 too slow. Multiple cores are avaible
There are many compression algorithms around, and bzip2 is one of the slower ones. Plain gzip tends to be significantly faster, at usually not much worse compression. When speed is the most important, ...
- 994
58
votes
Why do IOPS matter?
This is because sequential throughput is not how most I/O activity occurs.
Random reads/write operations are more representative of normal system activity, and that's usually bound by IOPS.
...
- 196k
44
votes
Accepted
Why is my bare-metal 16x 2.93GHz cores computer performing poorer than a VPS with 4x 2.5GHz cores?
Processor advancements, clock speed and IPC calculations can make it almost impossible to try to reasonably compare decade old CPUs to modern ones. Not only are the instructions per cycle going to ...
- 24.1k
43
votes
bzip2 too slow. Multiple cores are avaible
Use pbzip2.
The manual says:
pbzip2 is a parallel implementation of the bzip2 block-sorting file
compressor that uses pthreads and achieves near-linear speedup on SMP
machines. The output of ...
- 5,282
36
votes
Accepted
Why do IOPS matter?
Throughput
Throughput is useful when you're doing things like copying files. When you're doing almost anything else it's random reads and writes across the disk that will limit you.
IOPS
IOPS ...
- 31.2k
35
votes
Accepted
Delete 10M+ files from ZFS, effectively
Deletes in ZFS are expensive. Even more so if you have deduplication enabled on the filesystem (since dereferencing deduped files is expensive). Snapshots could complicate matters too.
You may be ...
- 196k
33
votes
Why does it take tens of seconds to get a shell prompt?
Quite a few things could be happening here. You can find most of the answers in your shell's manual, but those are usually incredibly long and oblique, so...
Chances are your problem boils down to ...
- 25.1k
32
votes
Why is my bare-metal 16x 2.93GHz cores computer performing poorer than a VPS with 4x 2.5GHz cores?
I don't want to sound terrible by emphasizing something that should be obvious here, but you're comparing a high-end server processor from 2014 to a high-end server processor from 2007.
I don't think ...
- 196k
30
votes
Accepted
Is it reasonable to use NFS on a production web server?
NFS is fine, barring some specific other criteria are met, namely:
The systems involved are both able to use NFS natively. Windows doesn't count here, it kind of works, but it's got a lot of quirks ...
- 2,195
29
votes
Delete 10M+ files from ZFS, effectively
How is it possible that resilvering the whole array takes an hour, but deleting from the disk takes 4 days?
Consider an office building.
Removing all of the computers and furniture and fixings ...
- 1,449
28
votes
Accepted
What are the performance implications for millions of files in a modern file system?
The reason one would create this sort of directory structure is that filesystems must locate a file within a directory, and the larger the directory is, the slower that operation.
How much slower ...
- 241k
25
votes
Accepted
What does "low profile" stand for, connected to hardware?
You have a few PCIe form factors:
You have different card and/or bracket heights:
FH - Full-height
HH - Half-height
And different card lengths:
FL - Full-length
HL - Half-lenth
"Low-profile" is ...
- 196k
25
votes
Should I be concerned that swap is being used on a host with nearly 40GB of free memory?
Linux will pre-emptively write out pages to disk if it has nothing better to do. That does not mean that it will evict those pages from memory, though. It's just that in case it must evict those pages ...
- 2,118
24
votes
Accepted
Why is FileZilla so much faster than PSFTP?
The FileZilla uses a PuTTY/psftp source code for an SFTP implementation. Actually the FileZilla runs a hidden PSFTP sub-process.
But it uses its own build of PSFTP (FzSFtp.exe) that employs few ...
- 7,544
24
votes
Accepted
Effect of distance from server
Assuming the graph is http request time it seems fairly reasonable to me.
A http request (in the absense of keepalive, fastopen etc) normally requires at least two round trips.
Client sends syn
...
- 4,106
23
votes
Accepted
Virtualization - Ten 1Gbps links or one 10Gbps link? (Performance)
1 x 10Gb link for performance.
Otherwise if a single server needs to use 1.1Gbs to another server it can't because most load balancing systems use destination MAC or IP (Which would be the same).
...
- 678
23
votes
Write speed requirement : 1.1GB/s possibilities?
For such extreme write speed, I suggest against ZFS, BTRFS or any CoW filesystem. I would use XFS, which is extremely efficient on large/streaming transfer.
There are many missing informations (how ...
- 45.5k
23
votes
Accepted
How to describe VMware performance requirements for our application to a VMware admin?
Seriously, most VMware administrators aren't good at this: Poor understanding of resource management, often no Linux knowledge (it helps) and lack of time bandwidth. I find most in-house admins have a ...
- 196k
23
votes
Accepted
What's the difference between a "degraded" RAID 6 array and a "clean" RAID 5 array?
Besides whatever metadata the RAID controller uses, are there any differences between these two arrays (in terms of data layout, performance, reliability)?
Yes. RAID5 uses a single, rotating parity ...
- 9,232
22
votes
Why does it take tens of seconds to get a shell prompt?
It's probably either waiting for DNS or trying to authenticate via LDAP or such.
Try to add UseDNS no to /etc/ssh/sshd_config
If it also does it on local logons, check if any LDAP servers or DNS ...
- 464
22
votes
Load time impact of htaccess
The recommendation from the Apache project is:
In general, you should only use .htaccess files when you don't have access to the main server configuration file. ... a common misconception is that ...
- 74k
19
votes
Accepted
Mysql showing 100% CPU usage
Looking at your details, we can conclude these general recommendations :
Your READ : WRITE ratio (61 : 39 ) gives the clue that your engine types should be changed to Innodb. Before that check the ...
- 656
19
votes
Accepted
Write speed requirement : 1.1GB/s possibilities?
Absolutely... ZFS on Linux is a possibility if architected correctly. There are many cases of poor ZFS design, but done well, your requirements can be met.
So the main determinant will be how you're ...
- 196k
18
votes
Accepted
SAS / SATA max number of connected disks vs performance
SATA/SAS are not like hubs, rather they work much like a network switch. This means that a single SATA/SAS port provides the entire advertised bandwidth, independently from the other ports.
In other ...
- 45.5k
18
votes
Effect of distance from server
Any other possible reason in addition to distance from server?
The path the packets take.
- 115k
18
votes
Accepted
Why don't servers always run at max?
Latency will be one reason. The lag between "disk give me this data I need before I can do anything else" and the time the data gets back will leave the CPU idle for that time.
Resources probably do ...
- 31.2k
18
votes
Is it reasonable to use NFS on a production web server?
NFS is absolutely OK and is preferred over iSCSI due to the fact NFS is much easier to manage, share and backup.
- 12.7k
17
votes
Accepted
Can mixing RAM memory size (on its own) reduce dual channel performance?
You will not be able to achieve dual channel performance with modules that are not identical.
What you get is called by intel FLEX mode.
That means, if the MB is good enough, you still get faster-...
- 3,018
Only top scored, non community-wiki answers of a minimum length are eligible