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bio website ripple.com
location Oakland, CA
age 44
visits member for 2 years, 10 months
seen 9 hours ago

I am Chief Cryptographer at Ripple Labs and one of the architects of the Ripple payment system.


Mar
3
comment Why does RAID5 with an odd number of data disks have poor write performance
After they split and join operations, do you think they wind up with more 2MB operations or 2.5MB operations?
Mar
3
comment Why does RAID5 with an odd number of data disks have poor write performance
So you're saying that bulk writes with sizes that are even multiples of 2.5MB are just as common as bulk writes that are multiples of 2MB? That seems a bit implausible to me.
Mar
3
comment Why does RAID5 with an odd number of data disks have poor write performance
@psusi: Whether it is 2MB or 2.5MB makes a reasonably significant difference. Requests from higher levels tend to be for aligned blocks. With 2.5MB blocks having to go out to the RAID, a higher fraction of writes won't be complete blocks and more writes will require a preceding read. Let me put it to you this way -- if we did a survey of write sizes from major applications, do you think more write clusters (sequential writes from the same source) would be multiples of 2MB in size or multiples of 2.5MB in size? Even if you use, say, a 1MB buffer, two buffers will fit perfectly.
Mar
3
comment Why does RAID5 with an odd number of data disks have poor write performance
How can a 4 disk RAID 5 array have a stripe size of 2MB? That would be 2/3MB per disk. If it writes, say 512KB per disk, that's 512KB*3 of data and 512KB of parity for each stripe.
Mar
3
comment Why does RAID5 with an odd number of data disks have poor write performance
You are confusing the block size with the stripe size. You can specify the block size, and it's independent of the number of disks (but must be a multiple of the drive's native block size). But then the stripe size will be, for RAID 5, the block size times the number of disks minus one. That's how RAID 5 works.
Mar
3
revised Why does RAID5 with an odd number of data disks have poor write performance
added 25 characters in body
Mar
3
comment Why does RAID5 with an odd number of data disks have poor write performance
No, the stripe size is not independent of the number of disks. If there are five disks, the stripe size must be four times the block size. That's how RAID 5 works and how it tolerates the loss of a disk. (It's n-1 for RAID 5, n-2 for RAID 6.) See Wikipedia. I explained what I meant by block size, "amount of user data that must be written to a drive as a unit". It can be any multiple of the disk's native size.
Mar
3
comment SSL Certificate Class 2 vs Class 3 vs Class 4
@jneff: GoDaddy has a CA they call "GoDaddy Class 2 Certification Authority". They can name their internal CAs anything they want. They can call it "GoDaddy Class Asparagus CA" if they want.
Mar
3
answered Why does RAID5 with an odd number of data disks have poor write performance
Mar
3
comment CNAME, A, and Apache - Why does one work and not the other?
@htg589: The whole point of the host header is to report the host the client asked for, not the host it actually wound up accessing. DNS resolves the host name to an IP address, whether by way of a CNAME or not is irrelevant.
Mar
2
comment vCPU and RAM for ESXi Server Scenario
I would never configure a VM with a single virtual CPU. For one thing, the MP version of modern OSes tends to be more stable. For another thing, it creates possible conversion pain.
Mar
2
comment Caching DNS. How does it choose what DNS server to query?
If you want it to ask specific nameservers, you can configure one or more forwarders. Usually this isn't a good idea though.
Mar
2
comment iptables rejects everything it should accept
You have no rule to allow outbound HTTP traffic. What good does it do to let requests in if responses can't get out?
Feb
29
comment GlassFish: There is a process already using the server port
GlassFish reports any bind failure with this message. You should treat it as just "bind to port XXXXX failed for some reason".
Feb
29
comment GlassFish: There is a process already using the server port
Does 127.0.0.1 work on the machine? Can you ping it?
Feb
29
comment How do certificates improve security?
Say you want to send credit car information securely to www.SomeMerchant.com. How do you know you're actually talking to guys at SomeMerchant.com and not some attacker who has hijacked your connection? That's the problem certificates solve.
Feb
29
answered mysql changes the IP when connecting
Feb
29
comment Should I add more RAM or CPU on my server? How do I figure this?
When your server is slow, is the CPU maxed? Is the disk maxed? Are both?
Feb
29
answered Will all cores be used on an i7 when running SQL Server 2008 R2 Standard
Feb
29
comment Does any USB controller card exist that fully offloads I/O from the host CPU?
@JonBailey: I doubt any mainstream chip does that (because it's no harder to do it better). They have to have a large enough buffer to hold a single DMA transaction, and then they always run that DMA transaction at the full speed of their own bus (assuming RAM can keep up). This will tie up the RAM bus, but either the DMA is fast (in which case it will be over soon) or it's slow (in which case the CPU can interleave). The CPU has caches so this shouldn't hurt it much.