Re: Question about EC2 and SSDs
Theory aside, I switched from RAID of ephemerals for data, and root volume for write log to single EBS-based SSD without any noticeable impact on performance. will On Thu, Sep 4, 2014 at 9:35 PM, Steve Robenalt sroben...@highwire.org wrote: Yes, I am aware there are no heads on an SSD. I also have seen plenty of examples where compatibility issues force awkward engineering tradeoffs, even as technology advances so I am jaded enough to be wary of making assumptions, which is why I asked the question. Steve On Sep 4, 2014 5:50 PM, Robert Coli rc...@eventbrite.com wrote: On Thu, Sep 4, 2014 at 5:44 PM, Steve Robenalt sroben...@highwire.org wrote: Thanks Robert! I am assuming that you meant that it's possible with a single SSD, right? Yes, no matter how many SSDs you have you are unlikely to be able to convince one of them to physically seek a drive head across its plater, because they don't have heads or platters. =Rob
Re: Question about EC2 and SSDs
EBS performance was a major concern a few years ago, but it's gotten better in the last few years with things like Provisioned IOPS and SSDs. However, it's still not recommended (reasons outlined here http://www.datastax.com/documentation/cassandra/2.0/cassandra/architecture/architecturePlanningEC2_c.html .) I personally don't care for EBS because of the reliability factor. Do a web search for EBS outage and you'll see that EBS has caused much pain for lots of organizations in the past. Ephemeral disks (which exist on the host of which your instance is running) will always be more reliable and generally are more performant. The trend seems to be that they're pushing people towards EBS (t2 instances are EBS only, other current gen instances are SSD only) and it's a shame. It's good to have choices. -Jared On 5 September 2014 13:51, William Oberman ober...@civicscience.com wrote: Theory aside, I switched from RAID of ephemerals for data, and root volume for write log to single EBS-based SSD without any noticeable impact on performance. will On Thu, Sep 4, 2014 at 9:35 PM, Steve Robenalt sroben...@highwire.org wrote: Yes, I am aware there are no heads on an SSD. I also have seen plenty of examples where compatibility issues force awkward engineering tradeoffs, even as technology advances so I am jaded enough to be wary of making assumptions, which is why I asked the question. Steve On Sep 4, 2014 5:50 PM, Robert Coli rc...@eventbrite.com wrote: On Thu, Sep 4, 2014 at 5:44 PM, Steve Robenalt sroben...@highwire.org wrote: Thanks Robert! I am assuming that you meant that it's possible with a single SSD, right? Yes, no matter how many SSDs you have you are unlikely to be able to convince one of them to physically seek a drive head across its plater, because they don't have heads or platters. =Rob
Question about EC2 and SSDs
Hi all, We are migrating a small cluster on AWS from instances based on spinning disks (using instance store) to SSD-backed instances and we're trying to pick the proper instance type. Some of the recommendations for spinning disks say to use different drives for log vs data partitions to avoid issues with seek delays and contention for the disk heads. Since SSDs don't have the same seek delays, is it still recommended to use 2 SSD drives? Or is one sufficient? Thanks, Steve
Re: Question about EC2 and SSDs
With SSD one drive should be sufficient for both data and commitLogs. Rahul Neelakantan On Sep 4, 2014, at 8:05 PM, Steve Robenalt sroben...@highwire.org wrote: Hi all, We are migrating a small cluster on AWS from instances based on spinning disks (using instance store) to SSD-backed instances and we're trying to pick the proper instance type. Some of the recommendations for spinning disks say to use different drives for log vs data partitions to avoid issues with seek delays and contention for the disk heads. Since SSDs don't have the same seek delays, is it still recommended to use 2 SSD drives? Or is one sufficient? Thanks, Steve
Re: Question about EC2 and SSDs
On Thu, Sep 4, 2014 at 5:05 PM, Steve Robenalt sroben...@highwire.org wrote: We are migrating a small cluster on AWS from instances based on spinning disks (using instance store) to SSD-backed instances and we're trying to pick the proper instance type. Some of the recommendations for spinning disks say to use different drives for log vs data partitions to avoid issues with seek delays and contention for the disk heads. Since SSDs don't have the same seek delays, is it still recommended to use 2 SSD drives? Or is one sufficient? The purpose of distinct mount points for commitlog and data is to allow the commitlog to operate in an append only manner without seeking. This is possible with SSD disk. =Rob
Re: Question about EC2 and SSDs
Thanks Rahul! That was my inclination, but I don't want to take things like that for granted. Anybody have a dissenting view? Steve On Thu, Sep 4, 2014 at 5:14 PM, Rahul Neelakantan ra...@rahul.be wrote: With SSD one drive should be sufficient for both data and commitLogs. Rahul Neelakantan On Sep 4, 2014, at 8:05 PM, Steve Robenalt sroben...@highwire.org wrote: Hi all, We are migrating a small cluster on AWS from instances based on spinning disks (using instance store) to SSD-backed instances and we're trying to pick the proper instance type. Some of the recommendations for spinning disks say to use different drives for log vs data partitions to avoid issues with seek delays and contention for the disk heads. Since SSDs don't have the same seek delays, is it still recommended to use 2 SSD drives? Or is one sufficient? Thanks, Steve
Re: Question about EC2 and SSDs
Thanks Robert! I am assuming that you meant that it's possible with a single SSD, right? On Thu, Sep 4, 2014 at 5:42 PM, Robert Coli rc...@eventbrite.com wrote: On Thu, Sep 4, 2014 at 5:05 PM, Steve Robenalt sroben...@highwire.org wrote: We are migrating a small cluster on AWS from instances based on spinning disks (using instance store) to SSD-backed instances and we're trying to pick the proper instance type. Some of the recommendations for spinning disks say to use different drives for log vs data partitions to avoid issues with seek delays and contention for the disk heads. Since SSDs don't have the same seek delays, is it still recommended to use 2 SSD drives? Or is one sufficient? The purpose of distinct mount points for commitlog and data is to allow the commitlog to operate in an append only manner without seeking. This is possible with SSD disk. =Rob
Re: Question about EC2 and SSDs
On Thu, Sep 4, 2014 at 5:44 PM, Steve Robenalt sroben...@highwire.org wrote: Thanks Robert! I am assuming that you meant that it's possible with a single SSD, right? Yes, no matter how many SSDs you have you are unlikely to be able to convince one of them to physically seek a drive head across its plater, because they don't have heads or platters. =Rob
Re: Question about EC2 and SSDs
On 5 Sep 2014, at 10:05 am, Steve Robenalt sroben...@highwire.org wrote: We are migrating a small cluster on AWS from instances based on spinning disks (using instance store) to SSD-backed instances and we're trying to pick the proper instance type. Some of the recommendations for spinning disks say to use different drives for log vs data partitions to avoid issues with seek delays and contention for the disk heads. Since SSDs don't have the same seek delays, is it still recommended to use 2 SSD drives? Or is one sufficient? As a side note, splitting the commit log and data dirs into different volumes doesn’t do a whole lot of good on AWS irrespective of whether you are on spinning disks or SSDs. Simply because the volumes presented to the vm may be on the same disk. Just raid the available volumes and be done with it. Ben Bromhead Instaclustr | www.instaclustr.com | @instaclustr | +61 415 936 359
Re: Question about EC2 and SSDs
Yes, I am aware there are no heads on an SSD. I also have seen plenty of examples where compatibility issues force awkward engineering tradeoffs, even as technology advances so I am jaded enough to be wary of making assumptions, which is why I asked the question. Steve On Sep 4, 2014 5:50 PM, Robert Coli rc...@eventbrite.com wrote: On Thu, Sep 4, 2014 at 5:44 PM, Steve Robenalt sroben...@highwire.org wrote: Thanks Robert! I am assuming that you meant that it's possible with a single SSD, right? Yes, no matter how many SSDs you have you are unlikely to be able to convince one of them to physically seek a drive head across its plater, because they don't have heads or platters. =Rob
