Are you guys talking about 5Mbytes/sec to each journal device? Even if you had 8 OSDs per journal and had 2000 osds... you would need a sustained 1.25 Gbytes/sec to average 5Mbytes/sec per journal device.
On Tue, May 2, 2017 at 1:47 PM Willem Jan Withagen <wjw@xxxxxxxxxxx> wrote:
On 02-05-17 19:16, Дробышевский, Владимир wrote:
> Willem,
>
> please note that you use 1.6TB Intel S3520 endurance rating in your
> calculations but then compare prices with 480GB model, which has only
> 945TBW or 1.1DWPD (
> https://ark.intel.com/products/93026/Intel-SSD-DC-S3520-Series-480GB-2_5in-SATA-6Gbs-3D1-MLC
> ). It also worth to notice that S3710 has tremendously higher write
> speed\IOPS and especially SYNC writes. Haven't seen S3520 real sync
> write tests yet but don't think they differ much from S3510 ones.
Arrgh, you are right. I guess I had too many pages open, and copied the
wrong one.
But the good news is that the stats were already in favour of the 3710
so this only increases that conclusion.
The bad news is that the sustained write speed goes down with a factor 4.
So that is 5Mbyte/sec. Which is real easy to obtain, even with hardware
0f 2000.
--WjW
> Best regards,
> Vladimir
>
> 2017-05-02 21:05 GMT+05:00 Willem Jan Withagen <wjw@xxxxxxxxxxx
> <mailto:wjw@xxxxxxxxxxx>>:
>
> On 27-4-2017 20:46, Alexandre DERUMIER wrote:
> > Hi,
> >
> >>> What I'm trying to get from the list is /why/ the "enterprise" drives
> >>> are important. Performance? Reliability? Something else?
> >
> > performance, for sure (for SYNC write, https://www.sebastien-han.fr/blog/2014/10/10/ceph-how-to-test-if-your-ssd-is-suitable-as-a-journal-device/
> <https://www.sebastien-han.fr/blog/2014/10/10/ceph-how-to-test-if-your-ssd-is-suitable-as-a-journal-device/>)
> >
> > Reliabity : yes, enteprise drive have supercapacitor in case of powerfailure, and endurance (1 DWPD for 3520, 3 DWPD for 3610)
> >
> >
> >>> Also, 4 x Intel DC S3520 costs as much as 1 x Intel DC S3610. Obviously
> >>> the single drive leaves more bays free for OSD disks, but is there any
> >>> other reason a single S3610 is preferable to 4 S3520s? Wouldn't 4xS3520s
> >>> mean:
> >
> > where do you see this price difference ?
> >
> > for me , S3520 are around 25-30% cheaper than S3610
>
> I just checked for the DCS3520 on
> https://ark.intel.com/nl/products/93005/Intel-SSD-DC-S3520-Series-1_6TB-2_5in-SATA-6Gbs-3D1-MLC
> <https://ark.intel.com/nl/products/93005/Intel-SSD-DC-S3520-Series-1_6TB-2_5in-SATA-6Gbs-3D1-MLC>
>
> And is has a TBW of 2925 (Terrabytes Write over life time) = 2,9 PB
> the warranty is 5 years.
>
> Now if I do the math:
> 2925 * 104 /5 /365 /24 /60 = 1,14 Gbyte/min to be written.
> which is approx 20Mbyte /sec
> or approx 10Gbit/min = 0,15 Gbit/sec
>
> And that is only 20% of the capacity of that SATA link.
> Also writing 20Mbyte/sec sustained is not really that hard for modern
> systems.
>
> Now a 400Gb 3710 takes 8.3 PB, which is ruffly 3 times as much.
> so it will last 3 times longer.
>
> Checking Amazone, I get
> $520 for the DC S3710-400G
> $300 for the DC S3520-480G
>
> So that is less than a factor of 2 for using the S3710's and a 3 times
> longer lifetime. To be exact (8.3/520) / (2,9/300) = 1.65 more bang for
> your buck.
>
> But still do not expect your SSDs to last very long if the write rate is
> much over that 20Mbyte/sec
>
> --WjW
>
>
>
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