On 08/05/12 14:55, Martin Steigerwald wrote: > Am Dienstag, 8. Mai 2012 schrieb Daniel Pocock: >> On 08/05/12 00:24, Martin Steigerwald wrote: >>> Am Montag, 7. Mai 2012 schrieb Daniel Pocock: >>>> On 07/05/12 20:59, Martin Steigerwald wrote: >>>>> Am Montag, 7. Mai 2012 schrieb Daniel Pocock: >>>>>>> Possibly the older disk is lying about doing cache flushes. The >>>>>>> wonderful disk manufacturers do that with commodity drives to make >>>>>>> their benchmark numbers look better. If you run some random IOPS >>>>>>> test against this disk, and it has performance much over 100 IOPS >>>>>>> then it is definitely not doing real cache flushes. >>>>> >>>>> […] >>>>> >>>>> I think an IOPS benchmark would be better. I.e. something like: >>>>> >>>>> /usr/share/doc/fio/examples/ssd-test >>>>> >>>>> (from flexible I/O tester debian package, also included in upstream >>>>> tarball of course) >>>>> >>>>> adapted to your needs. >>>>> >>>>> Maybe with different iodepth or numjobs (to simulate several threads >>>>> generating higher iodepths). With iodepth=1 I have seen 54 IOPS on a >>>>> Hitachi 5400 rpm harddisk connected via eSATA. >>>>> >>>>> Important is direct=1 to bypass the pagecache. >>>> >>>> Thanks for suggesting this tool, I've run it against the USB disk and >>>> an LV on my AHCI/SATA/md array >>>> >>>> Incidentally, I upgraded the Seagate firmware (model 7200.12 from CC34 >>>> to CC49) and one of the disks went offline shortly after I brought the >>>> system back up. To avoid the risk that a bad drive might interfere >>>> with the SATA performance, I completely removed it before running any >>>> tests. Tomorrow I'm out to buy some enterprise grade drives, I'm >>>> thinking about Seagate Constellation SATA or even SAS. >>>> >>>> Anyway, onto the test results: >>>> >>>> USB disk (Seagate 9SD2A3-500 320GB): >>>> >>>> rand-write: (groupid=3, jobs=1): err= 0: pid=22519 >>>> >>>> write: io=46680KB, bw=796512B/s, iops=194, runt= 60012msec >>>> >>>> slat (usec): min=13, max=25264, avg=106.02, stdev=525.18 >>>> clat (usec): min=993, max=103568, avg=20444.19, stdev=11622.11 >>>> bw (KB/s) : min= 521, max= 1224, per=100.06%, avg=777.48, >>>> >>>> stdev=97.07 cpu : usr=0.73%, sys=2.33%, ctx=12024, majf=0, >>>> minf=20 IO depths : 1=0.1%, 2=0.1%, 4=100.0%, 8=0.0%, 16=0.0%, >>>> 32=0.0%, >>> >>> Please repeat the test with iodepth=1. >> >> For the USB device: >> >> rand-write: (groupid=3, jobs=1): err= 0: pid=11855 >> write: io=49320KB, bw=841713B/s, iops=205, runt= 60001msec >> slat (usec): min=67, max=6234, avg=112.62, stdev=136.92 >> clat (usec): min=684, max=97358, avg=4737.20, stdev=4824.08 >> bw (KB/s) : min= 588, max= 1029, per=100.46%, avg=824.74, stdev=84.47 >> cpu : usr=0.64%, sys=2.89%, ctx=12751, majf=0, minf=21 >> IO depths : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >> >>> =64=0.0% >> >> submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >> >>> =64=0.0% >> >> complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >> >>> =64=0.0% >> >> issued r/w: total=0/12330, short=0/0 >> lat (usec): 750=0.02%, 1000=0.48% >> lat (msec): 2=1.05%, 4=66.65%, 10=26.32%, 20=1.46%, 50=3.99% >> lat (msec): 100=0.03% >> >> and for the SATA disk: >> >> rand-write: (groupid=3, jobs=1): err= 0: pid=12256 >> write: io=28020KB, bw=478168B/s, iops=116, runt= 60005msec >> slat (usec): min=58, max=132637, avg=110.51, stdev=1623.80 >> clat (msec): min=2, max=206, avg= 8.44, stdev= 7.10 >> bw (KB/s) : min= 95, max= 566, per=100.24%, avg=467.11, stdev=97.64 >> cpu : usr=0.36%, sys=1.17%, ctx=7196, majf=0, minf=21 >> IO depths : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, > […] >> issued r/w: total=0/7005, short=0/0 >> >> lat (msec): 4=6.31%, 10=69.54%, 20=22.68%, 50=0.63%, 100=0.76% >> lat (msec): 250=0.09% >> >>> 194 IOPS appears to be highly unrealistic unless NCQ or something like >>> that is in use. At least if thats a 5400/7200 RPM sata drive (didn´t >>> check vendor information). >> >> The SATA disk does have NCQ >> >> USB disk is supposed to be 5400RPM, USB2, but reporting iops=205 >> >> SATA disk is 7200 RPM, 3 Gigabit SATA, but reporting iops=116 >> >> Does this suggest that the USB disk is caching data but telling Linux >> the data is on disk? > > Looks like it. > > Some older values for a 1.5 TB WD Green Disk: > > mango:~# fio -readonly -name iops -rw=randread -bs=512 -runtime=100 -iodepth 1 > -filename /dev/sda -ioengine libaio -direct=1 > [...] iops: (groupid=0, jobs=1): err= 0: pid=9939 > read : io=1,859KB, bw=19,031B/s, iops=37, runt=100024msec [...]</pre> > > > mango:~# fio -readonly -name iops -rw=randread -bs=512 -runtime=100 -iodepth > 32 -filename /dev/sda -ioengine libaio -direct=1 > iops: (groupid=0, jobs=1): err= 0: pid=10304 > read : io=2,726KB, bw=27,842B/s, iops=54, runt=100257msec > > mango:~# hdparm -I /dev/sda | grep -i queue > Queue depth: 32 > * Native Command Queueing (NCQ) > > - 1,5 TB Western Digital, WDC WD15EADS-00P8B0 > - Pentium 4 mit 2,80 GHz > - 4 GB RAM, 32-Bit Linux > - Linux Kernel 2.6.36 > - fio 1.38-1 > >>>> The IOPS scores look similar, but I checked carefully and I'm fairly >>>> certain the disks were mounted correctly when the tests ran. >>>> >>>> Should I run this tool over NFS, will the results be meaningful? >>>> >>>> Given the need to replace a drive anyway, I'm really thinking about one >>>> of the following approaches: >>>> - same controller, upgrade to enterprise SATA drives >>>> - buy a dedicated SAS/SATA controller, upgrade to enterprise SATA >>>> drives >>>> - buy a dedicated SAS/SATA controller, upgrade to SAS drives >>>> >>>> My HP N36L is quite small, one PCIe x16 slot, the internal drive cage >>>> has an SFF-8087 (mini SAS) plug, so I'm thinking I can grab something >>>> small like the Adaptec 1405 - will any of these solutions offer a >>>> definite win with my NFS issues though? >>> >>> First I would like to understand more closely what your NFS issues are. >>> Before throwing money at the problem its important to understand what the >>> problem actually is. >> >> When I do things like unpacking a large source tarball, iostat reports >> throughput to the drive between 500-1000kBytes/second >> >> When I do the same operation onto the USB drive over NFS, I see over >> 5000kBytes/second - but it appears from the iops test figures that the >> USB drive is cheating, so we'll ignore that. >> >> - if I just dd to the SATA drive over NFS (with conv=fsync), I see much >> faster speeds > > Easy. Less roundtrips. > > Just watch nfsstat -3 while untarring a tarball over NFS to see what I mean. > >> - if I'm logged in to the server, and I unpack the same tarball onto the >> same LV, the operation completes at 30MBytes/sec > > No network. > > Thats the LV on the internal disk? Yes >> It is a gigabit network and I think that the performance of the dd >> command proves it is not something silly like a cable fault (I have come >> across such faults elsewhere though) > > What is the latency? > $ ping -s 1000 192.168.1.2 PING 192.168.1.2 (192.168.1.2) 1000(1028) bytes of data. 1008 bytes from 192.168.1.2: icmp_req=1 ttl=64 time=0.307 ms 1008 bytes from 192.168.1.2: icmp_req=2 ttl=64 time=0.341 ms 1008 bytes from 192.168.1.2: icmp_req=3 ttl=64 time=0.336 ms >>> Anyway, 15000 RPM SAS drives should give you more IOPS than 7200 RPM SATA >>> drives, but SATA drives are cheaper and thus you could - depending on >>> RAID level - increase IOPS by just using more drives. >> >> I was thinking about the large (2TB or 3TB) 7200 RPM SAS or SATA drives >> in the Seagate `Constellation' enterprise drive range. I need more >> space anyway, and I need to replace the drive that failed, so I have to >> spend some money anyway - I just want to throw it in the right direction >> (e.g. buying a drive, or if the cheap on-board SATA controller is a >> bottleneck or just extremely unsophisticated, I don't mind getting a >> dedicated controller) >> >> For example, if I knew that the controller is simply not suitable with >> barriers, NFS, etc and that a $200 RAID card or even a $500 RAID card >> will guarantee better performance with my current kernel, I would buy >> that. (However, I do want to use md RAID rather than a proprietary >> format, so any RAID card would be in JBOD mode) > > They point is: How much of the performance will arrive at NFS? I can't say > yet. My impression is that the faster performance of the USB disk was a red herring, and the problem really is just the nature of the NFS protocol and the way it is stricter about server-side caching (when sync is enabled) and consequently it needs more iops. I've turned two more machines (a HP Z800 with SATA disk and a Lenovo X220 with SSD disk) into NFSv3 servers, repeated the same tests, and found similar performance on the Z800, but 20x faster on the SSD (which can support more IOPS) >>> But still first I´d like to understand *why* its slow. >>> >>> What does >>> >>> iostat -x -d -m 5 >>> vmstat 5 >>> >>> say when excersing the slow (and probably a faster) setup? See [1]. >> >> All the iostat output is typically like this: >> Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s >> avgrq-sz avgqu-sz await svctm %util >> dm-23 0.00 0.00 0.20 187.60 0.00 0.81 >> 8.89 2.02 10.79 5.07 95.20 >> dm-23 0.00 0.00 0.20 189.80 0.00 0.91 >> 9.84 1.95 10.29 4.97 94.48 >> dm-23 0.00 0.00 0.20 228.60 0.00 1.00 >> 8.92 1.97 8.58 4.10 93.92 >> dm-23 0.00 0.00 0.20 231.80 0.00 0.98 >> 8.70 1.96 8.49 4.06 94.16 >> dm-23 0.00 0.00 0.20 229.20 0.00 0.94 >> 8.40 1.92 8.39 4.10 94.08 > > Hmmm, disk looks quite utilitzed. Are there other I/O workloads on the > machine? No, just me testing it >> and vmstat: >> >> procs -----------memory---------- ---swap-- -----io---- -system-- >> ----cpu---- >> r b swpd free buff cache si so bi bo in cs us sy >> id wa >> ... >> 0 1 0 6881772 118660 576712 0 0 1 1033 720 1553 0 2 >> 60 38 >> 0 1 0 6879068 120220 577892 0 0 1 918 793 1595 0 2 >> 56 41 >> 0 1 0 6876208 122200 578684 0 0 1 1055 767 1731 0 2 >> 67 31 >> 1 1 0 6873356 124176 579392 0 0 1 1014 742 1688 0 2 >> 66 32 >> 0 1 0 6870628 126132 579904 0 0 1 1007 753 1683 0 2 >> 66 32 > > And wait I/O is quite high. > > Thus it seems this workload can be faster with faster / more disks or a RAID > controller with battery (and disabling barriers / cache flushes). You mean barrier=0,data=writeback? Or just barrier=0,data=ordered? In theory that sounds good, but in practice I understand it creates some different problems, eg: - monitoring the battery, replacing it periodically - batteries only hold the charge for a few hours, so if there is a power outage on a Sunday, someone tries to turn on the server on Monday morning and the battery has died, cache is empty and disk is corrupt - some RAID controllers (e.g. HP SmartArray) insist on writing their metadata to all volumes - so you become locked in to the RAID vendor. I prefer to just use RAID1 or RAID10 with Linux md onto the raw disks. On some Adaptec controllers, `JBOD' mode allows md to access the disks directly, although I haven't verified that yet. I'm tempted to just put a UPS on the server and enable NFS `async' mode, and avoid running anything on the server that may cause a crash. >> and nfsstat -s -o all -l -Z5 >> >> nfs v3 server total: 319 >> ------------- ------------- -------- >> nfs v3 server getattr: 1 >> nfs v3 server setattr: 126 >> nfs v3 server access: 6 >> nfs v3 server write: 61 >> nfs v3 server create: 61 >> nfs v3 server mkdir: 3 >> nfs v3 server commit: 61 > > I would like to see nfsiostat from newer nfs-utils, cause it includes > latencies. > >>> [1] >>> http://xfs.org/index.php/XFS_FAQ#Q:_What_information_should_I_include_whe >>> n_reporting_a_problem.3F >> >> I've also tested onto btrfs and the performance was equally bad, so it >> may not be an ext4 issue >> >> The environment is: >> Linux srv1 3.2.0-0.bpo.2-amd64 #1 SMP Mon Apr 23 08:38:01 UTC 2012 >> x86_64 GNU/Linux >> (Debian squeeze) >> Kernel NFS v3 >> HP N36L server, onboard AHCI >> md RAID1 as a 1TB device (/dev/md2) >> /dev/md2 is a PV for LVM - no other devices attached >> >> As mentioned before, I've tried with and without write cache. >> dmesg reports that ext4 (and btrfs) seem to be happy to accept the >> barrier=1 or barrier=0 setting with the drives. > > 3.2 doesn't report failure on barriers anymore. Barriers have been switched to > cache flush requests and these will not report back failure. So you have to > make sure cache flushes work in other ways. > >> dmesg and hdparm also appear to report accurate information about write >> cache status. >> >>> (quite some of this should be relevant when reporting with ext4 as well) >>> >>> As for testing with NFS: I except the values to drop. NFS has quite some >>> protocol overhead due to network roundtrips. On my nasic tests NFSv4 even >>> more so than NFSv3. As for NFS I suggest trying nfsiostat python script >>> from newer nfs-utils. It also shows latencies. >> >> I agree - but 500kBytes/sec is just so much slower than anything I've >> seen with any IO device in recent years. I don't expect to get 90% of >> the performance of a local disk, but is getting 30-50% reasonable? > > Depends on the workload. > > You might consider using FS-Cache with cachefilesd for local client side > caching. > > Ciao, -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
