Re: Filesystem benchmarking for pg 8.3.3 server - Mailing list pgsql-performance
From | Greg Smith |
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Subject | Re: Filesystem benchmarking for pg 8.3.3 server |
Date | |
Msg-id | Pine.GSO.4.64.0808130150510.9761@westnet.com Whole thread Raw |
In response to | Re: Filesystem benchmarking for pg 8.3.3 server (Ron Mayer <rm_pg@cheapcomplexdevices.com>) |
Responses |
Re: Filesystem benchmarking for pg 8.3.3 server
|
List | pgsql-performance |
On Tue, 12 Aug 2008, Ron Mayer wrote: > Really old software (notably 2.4 linux kernels) didn't send > cache synchronizing commands for SCSI nor either ATA; but > it seems well thought through in the 2.6 kernels as described > in the Linux kernel documentation. > http://www.mjmwired.net/kernel/Documentation/block/barrier.txt If you've drank the kool-aid you might believe that. When I see people asking about this in early 2008 at http://thread.gmane.org/gmane.linux.kernel/646040 and serious disk driver hacker Jeff Garzik says "It's completely ridiculous that we default to an unsafe fsync." [ http://thread.gmane.org/gmane.linux.kernel/646040 ], I don't know about you but that barrier documentation doesn't make me feel warm and safe anymore. > If you do have a disk where you need to disable write caches, > I'd love to know the name of the disk and see the output of > of "hdparm -I /dev/sd***" to see if it claims to support such > cache flushes. The below disk writes impossibly fast when I issue a sequence of fsync writes to it under the CentOS 5 Linux I was running on it. Should only be possible to do at most 120/second since it's 7200 RPM, and if I poke it with "hdparm -W0" first it behaves. The drive is a known piece of junk from circa 2004, and it's worth noting that it's an ext3 filesystem in a md0 RAID-1 array (aren't there issues with md and the barriers?) # hdparm -I /dev/hde /dev/hde: ATA device, with non-removable media Model Number: Maxtor 6Y250P0 Serial Number: Y62K95PE Firmware Revision: YAR41BW0 Standards: Used: ATA/ATAPI-7 T13 1532D revision 0 Supported: 7 6 5 4 Configuration: Logical max current cylinders 16383 65535 heads 16 1 sectors/track 63 63 -- CHS current addressable sectors: 4128705 LBA user addressable sectors: 268435455 LBA48 user addressable sectors: 490234752 device size with M = 1024*1024: 239372 MBytes device size with M = 1000*1000: 251000 MBytes (251 GB) Capabilities: LBA, IORDY(can be disabled) Standby timer values: spec'd by Standard, no device specific minimum R/W multiple sector transfer: Max = 16 Current = 16 Advanced power management level: unknown setting (0x0000) Recommended acoustic management value: 192, current value: 254 DMA: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 udma5 *udma6 Cycle time: min=120ns recommended=120ns PIO: pio0 pio1 pio2 pio3 pio4 Cycle time: no flow control=120ns IORDY flow control=120ns Commands/features: Enabled Supported: * SMART feature set Security Mode feature set * Power Management feature set * Write cache * Look-ahead * Host Protected Area feature set * WRITE_VERIFY command * WRITE_BUFFER command * READ_BUFFER command * NOP cmd * DOWNLOAD_MICROCODE Advanced Power Management feature set SET_MAX security extension * Automatic Acoustic Management feature set * 48-bit Address feature set * Device Configuration Overlay feature set * Mandatory FLUSH_CACHE * FLUSH_CACHE_EXT * SMART error logging * SMART self-test -- * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
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