Date: Thu, 25 Jan 2007 10:50:38 -0800 From: Milo Hyson <milo@cyberlifelabs.com> To: freebsd-questions@freebsd.org Subject: RAID Performance Questions Message-ID: <25E0702D-C3A3-4B6B-BC56-D1BC5C1347F5@cyberlifelabs.com>
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I don't really have a whole lot of experience with RAID, so I was
wondering if the performance figures I'm seeing are normal or if I
just need to tweak things a bit. Based on what I've been reading, I
would expect more significant improvements over a single drive.
Here's my setup:
* FreeBSD 5.4-RELEASE-p22
* AMD Athlon 2200+
* 512 MB RAM
* 3ware 9500S-8 RAID controller
* 8 x Maxtor 7Y250M0 drives (SATA150 - 250 GB each)
* 1 x UDMA100 system drive
I'm using a trimmed-down but otherwise stock kernel (see below). The
array is configured as two units: a three-drive RAID 5 and a four-
drive RAID 10. Both units have been fully initialized and verified.
No errors or warnings are being issued by the controller --
everything is green. Using bonnie I get the following results with a
1.5 GB file:
-------Sequential Output-------- ---Sequential Input--
--Random--
-Per Char- --Block--- -Rewrite-- -Per Char- --Block---
--Seeks---
Machine MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %
CPU /sec %CPU
single 1536 42229 45.1 44379 19.4 17227 7.7 40819 41.6 44772 12.1
141.1 0.7
raid5 1536 21812 22.8 21876 8.7 12935 5.9 47283 48.3 61998 17.0
152.8 0.8
raid10 1536 21905 23.0 21999 8.6 14878 6.7 49036 50.1 64847 17.7
130.6 0.7
The write times of both RAID configurations are slower than the
single drive (which is expected due to having to write to multiple
drives). However, I wasn't expecting such a drastic reduction (about
50%). The read times, although faster, are only marginally so in per-
char transfer. They're a bit better in block performance, but still
not what I would expect. It would seem to me that a read spread
across four drives should see more than a 45% performance increase.
The highest rate recorded here is only a quarter of the PCI bus-
speed, so I doubt that's a bottleneck. CPU load peaks at 50%, so I
don't see that being a problem either.
I also ran some performance tests with a stock build of PostgreSQL
8.0 to get a different angle on things. Two tests were run on each of
the UDMA system drive, the RAID 5 unit, and the RAID 10 unit. The
first tested sequential-scans through a 58,000+ record table. The
second tested random index-scans of the same table. These were read-
only tests -- no write tests were performed. The results are as follows:
Unit Seq/sec Index/sec
------------------------------
single 0.550 2048.983
raid5 0.533 2063.900
raid10 0.533 2093.283
Any performance benefit of RAID in these tests is almost nonexistent.
Am I doing something wrong? Am I expecting too much? Any advice that
can be offered in this area would be much appreciated.
Here is my kernel config (the twa driver is loaded as a module):
machine i386
cpu I686_CPU
ident NAS-20070124
options SCHED_4BSD # 4BSD scheduler
options INET # InterNETworking
options FFS # Berkeley Fast Filesystem
options SOFTUPDATES # Enable FFS soft updates
support
options UFS_ACL # Support for access control
lists
options UFS_DIRHASH # Improve performance on big
directories
options NFSCLIENT # Network Filesystem Client
options NFSSERVER # Network Filesystem Server
options CD9660 # ISO 9660 Filesystem
options PROCFS # Process filesystem
(requires PSEUDOFS)
options PSEUDOFS # Pseudo-filesystem framework
options COMPAT_43 # Compatible with BSD 4.3
[KEEP THIS!]
options COMPAT_FREEBSD4 # Compatible with FreeBSD4
options SCSI_DELAY=15000 # Delay (in ms) before
probing SCSI
options SYSVSHM # SYSV-style shared memory
options SYSVMSG # SYSV-style message queues
options SYSVSEM # SYSV-style semaphores
options _KPOSIX_PRIORITY_SCHEDULING # POSIX P1003_1B real-
time extensions
options ADAPTIVE_GIANT # Giant mutex is adaptive.
device apic # I/O APIC
# Bus support. Do not remove isa, even if you have no isa slots
device isa
device pci
# ATA and ATAPI devices
device ata
device atadisk # ATA disk drives
device atapicd # ATAPI CDROM drives
options ATA_STATIC_ID # Static device numbering
# SCSI support
device scbus # SCSI bus (required for SCSI)
device da # Direct Access (disks)
# atkbdc0 controls both the keyboard and the PS/2 mouse
device atkbdc # AT keyboard controller
device atkbd # AT keyboard
device vga # VGA video card driver
# syscons is the default console driver, resembling an SCO console
device sc
# Floating point support - do not disable.
device npx
# Serial (COM) ports
device sio # 8250, 16[45]50 based serial ports
# PCI Ethernet NICs that use the common MII bus controller code.
# NOTE: Be sure to keep the 'device miibus' line in order to use
these NICs!
device miibus # MII bus support
device xl # 3com 10/100
# Pseudo devices.
device loop # Network loopback
device mem # Memory and kernel memory devices
device io # I/O device
device random # Entropy device
device ether # Ethernet support
device pty # Pseudo-ttys (telnet etc)
--
Milo Hyson
CyberLife Labs
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