On Thu, Apr 16, 2009 at 11:28 AM, Richard Elling <richard.ell...@gmail.com>wrote:
> As for space, 18GBytes is much, much larger than 99.9+% of workloads > require for slog space. Most measurements I've seen indicate that 100 > MBytes > will be quite satisfactory for most folks. Unfortunately, there is no > market > for small disk drives -- HDD or SDD. Let me see if I understand this: A SSD slog can handle, say, 5000 (4k) transactions in a sec (20M/s) vs maybe 300 (4k) iops for a single HDD. The slog can then batch and dump say 30s worth of transactions - 600M as one sequential write - say 15s (at 40M/s) for a single HDD. So maybe at most 2GB is needed for 60s worth of traffic. And this is the big win for sync NFS - .2ms latency vs 3+ms latency. For 4k NFS blocks at 3ms latency difference that is 10,000/4*3/1000 = 7.5 sec of extra latency for a 10M file. Ignoring all other latency issues. Not sure what the iops for a SSD is at 32k. But assuming, 3000 iops at 30k means 96M/s or 5GB for 60s. So for a 10MB file the latency difference at 32k is only 1 sec. Nicholas
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