USB Boot Drive - Speed Root cause

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penguinpages
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USB Boot Drive - Speed Root cause

Post by penguinpages » 2020/09/11 19:57:42

I have a three node cluster. Same system hardware. Same USB keys.. 64GB Sandisk Cruzer SDCZ50-64G

I noted that something is wrong with the one server. All commands and sessions take 50% longer to launch.. but the baseline seems that once the binary is loaded into RAM.. it then is same speed on all systems... so I think this is a disk issue.

# Baseline System with good response
[root@thor ~]# hdparm -Tt /dev/sda

/dev/sda:
Timing cached reads: 24294 MB in 1.99 seconds = 12215.61 MB/sec
Timing buffered disk reads: 1498 MB in 3.00 seconds = 499.32 MB/sec
[root@odin ~]# lsmod |grep usb
usb_storage 73728 3 uas

# System with issue
[root@odin ~]# hdparm -Tt /dev/sda
[root@odin ~]# lsmod |grep hci
ahci 40960 4
libahci 40960 1 ahci
libata 270336 2 libahci,ahci

/dev/sda:
Timing cached reads: 19770 MB in 1.99 seconds = 9946.69 MB/sec
Timing buffered disk reads: 1504 MB in 3.00 seconds = 501.22 MB/sec
[root@odin ~]# lsmod |grep usb
usb_storage 73728 3 uas
[root@odin ~]# lsmod |grep hci
ahci 40960 4
libahci 40960 1 ahci
libata 270336 2 libahci,ahci


Maybe I am running down rathole .. I remember having issues with USB1 vs 2 where it would load up UHCI vs EHCI. I guess I will rule out hardware and DD image to a different spare key.. but think it kind of weird like I am missing something obvioius.

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TrevorH
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Re: USB Boot Drive - Speed Root cause

Post by TrevorH » 2020/09/12 13:39:36

I am about 99% sure that your USB key is not /dev/sda as that model of Sandisk says it's USB 2.0 which has a maximum bandwidth of 480MBps or 503316480bps which is 62914560 bytes/s or roughly 60MB/s. By the time you take in USB overheads, that will drop to about 40-45MB/s so there is no way you can ever get 500MB/s from a USB 2.0 stick.

To get throughput of 500MB/s like your hdparm output shows you would need to be using a USB 3.x USB stick in a USB 3.x socket. That has bandwidth starting at 5000Mbps (625MB/s).
CentOS 6 will die in November 2020 - migrate sooner rather than later!
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 is dead, do not use it.
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penguinpages
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Re: USB Boot Drive - Speed Root cause

Post by penguinpages » 2020/09/13 12:52:24

Your correct... my post was for wrong block device.

[root@thor ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 931.5G 0 disk
└─WDC_WDS100T2B0B-00YS70_19106A802926 253:3 0 931.5G 0 mpath
sdb 8:16 0 931.5G 0 disk
└─WDC_WDS100T2B0B-00YS70_192490801828 253:4 0 931.5G 0 mpath
└─WDC_WDS100T2B0B-00YS70_192490801828p1 253:5 0 931.5G 0 part
sdc 8:32 0 477G 0 disk
sdd 8:48 1 57.3G 0 disk
├─sdd1 8:49 1 1G 0 part /boot
└─sdd2 8:50 1 56.3G 0 part
├─cl-root 253:0 0 35.2G 0 lvm /
├─cl-swap 253:1 0 4G 0 lvm
└─cl-home 253:2 0 17.2G 0 lvm /home
[root@thor ~]# hdparm -Tt /dev/sda

/dev/sda:
Timing cached reads: 24400 MB in 1.99 seconds = 12268.94 MB/sec
Timing buffered disk reads: hdparm -Tt /dev/sd1462 MB in 3.00 seconds = 486.86 MB/sec
[root@thor ~]# hdparm -Tt /dev/sdd

/dev/sdd:
Timing cached reads: 23002 MB in 1.99 seconds = 11562.15 MB/sec
Timing buffered disk reads: 54 MB in 3.01 seconds = 17.93 MB/sec
[root@thor ~]#


But the other server is still showing same symptom. 5x slower then the others. I grabbed new key and tried to do fresh OS load and is taking forever..... Digging into UEFI version or flash or some wierd rathole. Will post back If I learn more.

Thanks for response

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TrevorH
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Re: USB Boot Drive - Speed Root cause

Post by TrevorH » 2020/09/13 16:44:57

The only thing that I see odd there is the mention of 'mpath' on the first two disks.
CentOS 6 will die in November 2020 - migrate sooner rather than later!
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 is dead, do not use it.
Full time Geek, part time moderator. Use the FAQ Luke

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