Re: Raid 5 vs Raid 10 Benchmarks Using bonnie++
От | Mark Kirkwood |
---|---|
Тема | Re: Raid 5 vs Raid 10 Benchmarks Using bonnie++ |
Дата | |
Msg-id | 4E4DB552.2050605@catalyst.net.nz обсуждение исходный текст |
Ответ на | Re: Raid 5 vs Raid 10 Benchmarks Using bonnie++ (Mark Kirkwood <mark.kirkwood@catalyst.net.nz>) |
Список | pgsql-performance |
On 19/08/11 12:52, Mark Kirkwood wrote: > On 19/08/11 02:09, Ogden wrote: >> On Aug 18, 2011, at 2:07 AM, Mark Kirkwood wrote: >> >>> On 18/08/11 17:35, Craig Ringer wrote: >>>> On 18/08/2011 11:48 AM, Ogden wrote: >>>>> Isn't this very dangerous? I have the Dell PERC H700 card - I see >>>>> that it has 512Mb Cache. Is this the same thing and good enough to >>>>> switch to nobarrier? Just worried if a sudden power shut down, >>>>> then data can be lost on this option. >>>>> >>>>> >>>> Yeah, I'm confused by that too. Shouldn't a write barrier flush >>>> data to persistent storage - in this case, the RAID card's battery >>>> backed cache? Why would it force a RAID controller cache flush to >>>> disk, too? >>>> >>>> >>> If the card's cache has a battery, then the cache is preserved in >>> the advent of crash/power loss etc - provided it has enough charge, >>> so setting 'writeback' property on arrays is safe. The >>> PERC/SERVERRAID cards I'm familiar (LSI Megaraid rebranded models) >>> all switch to write-though mode if they detect the battery is >>> dangerously discharged so this is not normally a problem (but >>> commit/fsync performance will fall off a cliff when this happens)! >>> >>> Cheers >>> >>> Mark >> >> So a setting such as this: >> >> Device Name : /dev/sdb >> Type : SAS >> Read Policy : No Read Ahead >> Write Policy : Write Back >> Cache Policy : Not Applicable >> Stripe Element Size : 64 KB >> Disk Cache Policy : Enabled >> >> >> Is sufficient to enable nobarrier then with these settings? >> > > > Hmm - that output looks different from the cards I'm familiar with. > I'd want to see the manual entries for "Cache Policy=Not Applicable" > and "Disk Cache Policy=Enabled" to understand what the settings > actually mean. Assuming "Disk Cache Policy=Enabled" means what I think > it does (i.e writes are cached in the physical drives cache), this > setting seems wrong if your card has on board cache + battery, you > would want to only cache 'em in the *card's* cache (too many caches > to keep straight in one's head, lol). > FWIW - here's what our ServerRaid (M5015) output looks like for a RAID 1 array configured with writeback, reads not cached on the card's memory, physical disk caches disabled: $ MegaCli64 -LDInfo -L0 -a0 Adapter 0 -- Virtual Drive Information: Virtual Drive: 0 (Target Id: 0) Name : RAID Level : Primary-1, Secondary-0, RAID Level Qualifier-0 Size : 67.054 GB State : Optimal Strip Size : 64 KB Number Of Drives : 2 Span Depth : 1 Default Cache Policy: WriteBack, ReadAheadNone, Direct, No Write Cache if Bad BBU Current Cache Policy: WriteBack, ReadAheadNone, Direct, No Write Cache if Bad BBU Access Policy : Read/Write Disk Cache Policy : Disabled Encryption Type : None
В списке pgsql-performance по дате отправления: