RAID Performance Questions
Martin Hepworth
maxsec at gmail.com
Thu Jan 25 19:40:14 UTC 2007
Milo
if you hunt around you should see papers/articles where it shows foe RAID 5
you need at least 5 drives before you any dramatic performance gains..(sun
old Sun articles from around 1998 where they do the math as well).
not sure about RAID 10, but again I *think* you need at least 3 drives in
the stripe before you start hitting gains.
To best test I'd put ALL the SATA drives into the RAID 5 or RAID 10 array
and then see what happens.
--
Martin
On 1/25/07, Milo Hyson <milo at cyberlifelabs.com> wrote:
>
> 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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